Next steps: send him back to his BM. I know he told you a sob story about having to do the dishes and showering before 9pm but trust if and when he moves in with you,you will find out why all these rules were in place and that there are some truths and some lies in the mix

IMO, you should follow the court order and your SS should get counseling with his BM to work on their relationship

If you want to go the custody route, all you have to do is file for modification and if both parties agree, the modification will be settled at a hearing and an updated court order will be issued.

 If both parties disagree, then be prepared to spend thousands in lawyer fees and court battles only to have SS decide to change his mind and stay with BM when he finds out that life at yours is just as hard and strict.

I think things need to calm down first. Then sit SS down and let him know that you care and hear him about his frustrations, but him living with you full time will come with some ground rules, and if you seek custody and pay the costs to get it, he must remain with you until age 18 or finished high school no matter what. He cannot flip flop back and forth whenever he doesn't like the rules.

So fast is saying something.  Most BM will understand that SS is trying out his new freedom.  That would let SS live with you for a time.  Is BM so dependent on CS  [Thet losing CS.  Maybe all of that . One kid with you, one with her equals no support ?  ] will make her get a job, or give up Uber eats ?   Or is she a control freak?  
Just be careful you are not in a one upmen game.  

Idk how bad things really are for SS at BM's, so disregard the rest of this if there really is abuse or neglect. But - when my kids were around middle-school age, they each did a similar thing while at their dad's, who i had 50/50 with. It was around 13-14 years old, same as with you. I drove over and sat outside and heard their case. I determined that, while what their dad did was a d!ck move (he was and still is a giant a-hole), it didn't warrant taking custody and the ensuing drama.

To a young teen, everything is an emergency. If you allow them to ping-pong back and forth based on which parent they are mad at and who lets them get away with the most, it isn't good for their development as people. The drama, the villain and rescuer role, the sympathy and honeymoon period, the inevitable falling out, rinse and repeat. Like i said, if there is actual abuse or neglect disregard this. But if he stays with you fulltime, don't let him get away with too much just because you feel sorry for him. 

This isn't your battle with the co-parent stuff... but as an outsider I genuinely would encourage your SO to stop intervening and encourage his son to spend parenting time with each parent.  Being asked to do dishes and shower before 9 pm doesn't sound in any way abusive... he will have the rest of his life to chose which parent he prefers to spend time with when he is an adult, but at 14 If both are willing to show up, and there is a functional custody arrangement already in place, I don't think a 14 year old preferring one place over the other should carry any weight on how parenting time works.

A kid's ability to choose which parent they want to live with... is not a thing. Some jurisdictions do not allow a Judge to hear from the minor child. Some jurisdictions allow the Judge to hear the kid's wishes though that is at the Judge's discretion.  No Jurisdiction allows the kid to choose as the final step.  The Judge is the final step for setting custody/CP/NCP structure.

This is all a good thing for SS and for your side.  SS is a kid, but... he seems to be intellgent and has put a lot of thought into his sitatuion before calling his father to come pick him up from school.  I would make sure that the CO is updated.  Since BM has threatened in front of the police to withhold visiation with the YSD, make sure to put those LEOs on the stand to testify to that.   Even if SS refuses to visit his BM, she cannot withhold the other kids from their father.   BM can call the police, they will come investigate, SS can refuse to go with her, DH can state clearly to SS, BM, and the LEOs that SS should visit his mother as COd to do so.  If BM withholds, that is an entirely different thing than a teen refusing.

DH needs to be ready to rip BM's throat out (figuratively) and defend his rights to all of his kids.  

SS is at the age where he may refuse to be BM's beck and call boy.  If they are piling dishes while he is with his father and then trying to force SS to clean up after BM and whatever man of the moment and Lord knows how many StepSibs, etc, I get SS's refusal to kiss their asses.

Normally, I would advise that SS be held to the schedule, but, at this stage a growingly confident young man is establishing his own standards for how he will be treated.  Admirable on one level. Risky on another level. But.... I applaud SS for calling mommy's bullshit and that she plied her usual manipulative crap in front of the LEOs..... Bonus!

Get your strategy built, compile extensive information, and be ready to rip out BM's throat in front of the Judge if she decides to take it to court.

In our experience, always being prepared is a small investment to drive rapid resolution.  And, it is better to have it and not need it, than need it and not have it.  

IMHO the challenge in the current situation is balancing what is best for SS with keeping to the CO and keeping BM under control.  Be very cognizant of all of the potential variables and prepare for them.  Adjust as necessary.

Shop for the right lawyer.  We fired our SpermLand lawyer who was far more interested in preserving her local relationships than delivering on our expectations.  She was not a bad lawyer, she was just too worried about sucking Judge ass, playing buddy with whatever bottom feeder lawyer the SpermClan brought in, a  different one regularly, and not upsetting the small town county seat community. I get that part, but we did not give a shit about anything but protecting SS's well being and defending DW from the SpermClan.

When we started shopping for our long term attorney, we made consulation appointments with several of the most recommended attorneys in our community.  We found our killer shark lawyer.  

When we were meeting with him he asked several very clear questions.

1. What are you trying to accomplish?

2. Are you doing this for the good of the kid or to punish BioDad?

3. If I do not believe that what you are trying to accomplish is either the right thing or possible, will you consider my alternative recommendations?

4. Custody/Visitation/Support actions can take time and can get expensive. Are you prepared and able to work on this over the long term and can you afford it?

We wrote him a retainer check on the spot. He was our attorney for two decades.

He once shared that we had not turned out to the the big revenue case he had hoped we were when we first met, but that he appreciated all of the clients that we referred him to.  He became the attorney on retainer for a number of friends and neighbors.  My college BFF and his wife did their adoption through our attorney, our across the street neighbors/friends used him on a multi year battle wiht the homeowners association, we did our Wills through him, several of our friends did their Wills through him, and when SS-31 asked me to adopt him when he was 22, our Shark did that for us too.

Find the right attorney that has the clear understanding that they work for you, their role is to deliver on your expectations and to advise and guide on any adjustments and changes that unfold.  Like a doctor, accountant, therapist, etc... your attorney works for you.  If they are not delivering to your expecation, fire them and find one who will.

Far too many people engage a lawyer without having specific goals that their attorney is to deliver to.  Don't do that.

Good luck.

Do you want SS to,live with you full time, ?  A lot different then EOW.  And BM Is not giving up CS.  She lives on that money,  It is going to make her life different.  In a bad way 

SD13 has a similar sob story about BM every couple of months. It will be time for SD13 to go to BM and she will start with the dramatics of "I just can't do this anymore." "BM doesn't treat me like a real person." "All she does is yell at me." etc. etc. etc.

DH fell for it (many a times) and repeated everything back to BM. She agreed, BM said YES I did yell at SD because she was being a brat. She REFUSED to go into a restaurant with us and said she was going to sit in the car, so I yelled "get your @ss out here now". 

Honestly, if I were SD13's bio mom, I would have done the same myself. SD13 was causing a scene and trying to ruin everyone's night out at a family dinner. She rightfully got called out on her BS. Do I think this warrants SD13 wanting to live with us full time? Heck no. But I can attest that when DH DOES fall for SD13s antics, all it does it lead to drama. Sticking to the CO is what is best for us. IMHO atleast. 

If you DO think there is some sort of abuse going on, then definitely take it seriously. But a BM can't have custody time taken away just because of "he said, she said", etc. Also, keep in my SK is already 14. By the time a custody case were to finish he might already be 16. No use making a mountain our of a mole hill THIS late into the game. 

It sounds like BM is somewhat strict on some of her rules.. but that doesn't necessarily make her a bad parent.. With 3 kids.. her (a SO too?).. I imagine ensuring that everyone keeps to a schedule in the home is important.

Reading between the lines.. I bet the dishes were waiting as a consequence.. either he skipped out when he left without doing them.. or some other issue.. like the going outside the fast food.. which at his age.. he knows the rule..  he broke it.. and in what century does it take that long to do the dishes.. even if by hand.. unless he got home at 8:45.. he probably had time.. AND.. he takes a shower at night and in the AM?  skipping one of those is not going to be the end of the world.. she isn't depriving him of some basic need in a way that is damaging.

And.. I am also guessing the 9pm is set for a reason.. other people in the home.. maybe she has to get up super early and goes to bed early and the sound of him showering is disturbing her.. or the other kids sleeping.. maybe he is at that age where he over lingers in the shower.. and that is disruptive?

I can see giving him a safety outlet when he and BM are at total odds.. but unless BM is outright abusive.. her being upset because he isn't living up to her standards.. is not necessarily a bad thing.  Bad grades.. bad actions.. bad paths being followed.. a good parent IS upset at their kid.. and tells them they will be in a bad way to continue.. does it make him feel warm and fuzzy to be called out? no.. maybe he needs to follow the rules better.. if you truly feel that they are overly restrictive.. none of the kids should be with her.. call CPS/

BM being a control freak.  Kids slaking off ...they all do..  7 people in BM house?   There are good reasons for BM rules, in her mind.  It has to be hard living with 6 other people.  Lot easier living with 2 other people.  

 If his kid calls and says he's not comfortable going to BMs, SO is not just gonna tell him he's out of luck. 

---------------------------------

Interesting choice of words you wrote that dh's kid is "not comfortable". 

Anyway, something is off here,,,my radar is pinging. 

BM's 'rules' are not unreasonable. When families have kids, shower times and bath times are essential to running the home smoothly, verses, flying by the seat of your pants.  Who cares if BM said no showers after 9pm.  It is not that hard to jump in the shower at 830pm. 

You have a lot to say about the rules topic and yet, nothing that remotely reads 'bm refuses access to showers and withholds all personal hygiene practices as punishment when he disobeys her. . (THAT would be something the courts would raise eye brows about) Telling a  kid to shower before 9pm is not it.

About bm asking your boyfriends kid to stand inside the restaurant until she arrived.  Nothing wrong with telling kid, HEY stay inside until I get there. Sure beats the kid running around the parking lot,, dashing out between cars. Teens can act stupid---trying to show off.  I see this as a safety measure on her part.  

Dad should be telling his boy...hey, take your shower before 9pm or LOOSE it. . If your mom tells you to stay inside until she arrives, ..do it. 

Does the teen follow the rules at school OR  call dad and say PICK UP ME I am uncomfortable?  Does kid play sports? Does he follow the teams rules? Or does he tell dad---come get me, I am uncomfortable. Does he complain about all the rules he has to follow, school, sports, his friends parents family home rules ...OR it is only MOM"S rules, in moms house, that he is uncomfortable about? 

Ping ping ping.