They're both adults. All of your expectations are reasonable.

Will it be a problem for your DH to:

• A) agree to all, or
• 2) pick up their slack?

This line: He mentioned it as "juicy gossip", but my heart sank as soon as I heard the news. I could see my DH telling me something like this one day like its no big deal meanwhile for me it would devastate me! I know though that we would not survive SD living here full time. Lucky for me I have made that very clear to DH for years so either this will never happen or if it does he will not be surprised when I leave. 

As for your ideas - All of those things shoufl have already been happening. AT 14 I had SD start doing her own laundry.At 16 SD got her own car. Her things have always stayed in her room, not all over the house. She keeps her room and the bathroom she uses clean and starting at 17 she gets her own dinners at least half of the nights she is with DH (about 5 out of 10 a month)

Why is the 23 year old working only part time? She needs a full time job and a place of her own. This is a great time for her to launch. DH needs to tell her that, help her make a plan if necessary, and maybe even help financially with deposit and first month's rent if you can afford it. She can visit and have meals now and then when invited. But it's not her house.

Then your only problem is the younger one, who might still want to spend summers and breaks from uni with Mom, or at least some of the time. If she is with you for extended periods, then, yes, she needs to respect house rules, take care of her own space and belongings, and contribute to the household through a reasonable amount of chores. She's an adult and should have adult expectations.

No freeloaders. Once that starts, you never get them out.

I'm with Merry - 23 yo gets 6 months to find her own place, period. There is no reason she should transfer her failure to launch from BM's house to yours.  She can get a full-time job and move in with roommates, or move with BM.

21 yo can stay there on breaks but is responsible for herself and does chores, etc.  She too is expected to have a full-time job upon graduation and make a plan to move out on her own. 

Maybe you will get lucky and they will go with BM.

I moved back into my mom and SF's house in my mid-20s as I was getting divorced. A few things they did that I agree with (and made me stay on track to move TF out as soon as possible):

1.) They charged me rent. Their rent was cheaper than if I were on my own, but I was financially in a hole. In your situation, I'd charge at least OSD a hefty sum, both to force her to learn budgeting and make her realize (combined with the other rules) that should could live with peers with fewer rules for less. If you don't need the cash to offset their expenses, save it and give it back to OSD when she moves out for her deposit, furniture, etc.

2.) My rent paid for my room, no where else in the house. It didn't cover my groceries. It didn't mean I could use the living room when my parents were home. It didn't allow me to have tons of friends come over. My parents were doing me a favor by giving me a cheap place to stay, but it was their place. Their comfort came first.

3.) I had to pay for all my stuff. Sure, they'd make me an extra plate at dinner, but I had to buy any special food I wanted. My toiletries were my responsibility. Car insurance, cell phone, health insurance, etc were all mine to pay for. There was no adding me to their family plan or any of that. I think I even had my own renter's policy since they were also renting.

4.) I had street parking. No primo parking for me. Their ability to use their driveway trumped me.

5.) They gave me a deadline by when I needed to get out, and my SF is the one who held me to it. I had to ask him to stay for a few extra months because I kept getting outbid on houses. But he is the one who kept me on track because my mom would have just said "oh, I'm sure she's doing enough" and let me slide. He wouldn't.

6.) They wanted proof that I was on track to move out. Showed them my paid off credit card. Told them who my realtor was when I went to buy a house. Talked about how much I had in savings. Part of this was guidance, but part of this was a reminder that they weren't kidding when they said I had X time and they were going to stick closely to that whether I was ready or not.

I hated every minute of living with them, but I also had been "free" for several years before I came back. You're in a slightly different boat because your OSD hasn't experienced freedom yet. So, treat her like a combination of a teenager and roommate. She has responsibilities like an adult does, but if she is living at home, she's going to be treated like she's a teenager who still needs guidance to launch. And your DH should provide that guidance and appropriate discipline. Adult kids need a soft place to land; what they don't need is to be coddled. A soft place to land means you get love and support from the people you live with, not free room and board until the end of time. Your SDs will benefit from food in the fridge, furniture in the house, internet and utilities, and less housework than if they were on their own or with roommates. That's more than enough support for adults.

A small caveat with your YSD: since she is in school, I would take a softer approach than with OSD. YSD is taking steps to better her life, and that should be rewarded so she is encouraged to keep trying to do better. That can ne reflected by not charging her rent, adding her to the family phone plan, etc. She still needs to do chores and buy her own food and toiletries, but I'd give her more leeway than OSD since she is a part-time resident who is actively working to launch.

How do you know that your DH wants SD21 to live with you between terms? Did he actually say that?

I'm a worrier and an overthinker, so the not knowing is what would give me anxiety.

I vote for taking the bull by the horns, and asking where the SDs plan to live. It's okay to admit you're not comfortable with having them in your home; that it's bad for your mental health, and that you worry it will put a strain on your relationship, BUT are willing to work on a compromise with him. If the two of you can put together a list of house rules, responsibilities, and RENT amount, that would be great.

I think that you should first and foremost have an honest talk with DH about how you're feeling.   Sit him down and make him understand that this is an important issue that requires his full attention.   The idea of your SDs moving in to your home is not a question of  "could" but rather it "will" change the dynamic of your relationship with your DH.  It will change how you and your DH relate to each other.  Neither of you can pretend that bringing someone, ANYone into your home, will not have an impact on your relationship.  It's just human nature.  

The next issue is that, where you once were able to, I don't know...sing at the top of your lungs to Fleetwood Mac, or run around the house in your underwear on laundry day, or talk freely and at will on the phone without fear of being overheard, well, those days will be gone.  When you come home from work, and you're in a not so great mood, and you're tired; now you'll have THREE personalities to have to navigate around.   How is any of that fair to you?  

And why have these ladies not "launched" yet.  Okay, so one is in University.  Fine.  When I did post secondary, I lived one and a half hours away from my parents, but I RENTED my own room in a house with other people, and I survived...and I was only 18!  I keep hearing that things are different now, but I don't quite understand why. 

If this is something that you really don't want to happen, you have to tell him that it's not a good idea because mentally and emotionally you're not prepared to share your home with anyone else at this stage in your life.  Your home is where you go to find complete security, peace and respite from everything. 

If it were me, I would probably tell my DH that if they are seriously moving in, I may have to seriously consider renting my own place where I can go to find peace when needed.  But that's just me...!

I moved back home for about 6 months after my divorce, and my mom took on the role of Lt. Dad's SF, ensuring the arrangement was as temporary as possible. I was miffed at the time, but i now credit her for my independence and the fact that (unlike my sister who, along with her kids, is coddled by my dad) I can manage my own kids without excessive "help."

I think the part about rent including your room goes a long way toward making the arrangement less invasive. Having an adult child (or, let's face it, any skid) and/or their friends taking over the living room or other common areas, or messing up the common areas, is a big part of why stepparents resent the presence of skids. A guilty daddy won't enforce that, though. They like the presence of their kids in common areas. Hell, i like the presence of my bios too, and I'm comfortable telling them to go to their rooms or outside if i need the area or want peace. Not so with a skid. That's just the way it is. Most people tolerate their own much more than someone else's. 

My SO just informed me that he wants to have his 22-year-old daughter move back in rent-free for the next 1-2 years. She couldn't make it on her own even with a roommate and him sending her about $100 a week. Her grandmother also couldn't deal with her, and at least one apartment complex either kicked her out or charged extra due to her neglect of her pets to the point that the excrement everywhere was grossing out the other tenants. One of her pets died under "mysterious circumstances", which i suspect was neglect. The story she told was lacking in detail and focused on how unfair they were, and she rarely tells the whole truth.

She lies pathologically, steals, and is at best a pothead as far as drugs go. She is very emotional and still has screaming tantrums. She has grandiose ideas about her future. States she is going to own multiple, multinational engineering firms but can't pass community college math or keep a job at a restaurant or big box store. I don't live there but i sleep over when my daughter is at her dad's, about 40-50 percent of nights. I don't think i can live with SD22, though, any percentage of the time. I thought about making a post about this, but there's not much advice to be given that hasn't been given in this thread.

SO asked for my advice on how to make it "work." I will suggest the no taking over common areas thing, but tbh, his other kids already do that, and the living room is pretty much their video game room 24/7. That's part of the reason his house will never feel like "home" to me. 

I suggested making sure she has a launch plan. He is thinking of having her do a community college program, something that will have her career-ready within 2 years. Making sure she is actually going to class and passing.

As for my own kids, after 18, they can live at home if they are going to school full-time and progressing toward a degree that will make them self-supporting. That's my boundary. My son didn't take me up on it, though, and lives at school about an hour away. He has a scholarship for full tuition and my dad helps with fees and living expenses that i can't cover (which is honestly most of it.) My son has been working part-time on and off but his "job" is to get through school on time. My dad's criteria for help is also that he goes to school full-time and progresses toward his degree on schedule. I wouldn't abide a 23-year-old, not in school, and working only part-time. That one needs to work full-time and have a timeframe for her to save up and be out, IMO. Good luck. Remember it's your house too. 

She is an adult - she needs to find her own housing or she can move across the country with BM.

The 21 year old - she is in college so its understandable that she needs housing in between semesters.  I would be fine with that - but as others have said - there are basic rules and contributions to the house she would have to make.  Even with that - I won't lie it does suck and was quite stressful to have SD (now 24) Bratty McBratFace stay with us a summer between school terms.  But we did get through it.

Also - make sure DH and you agree that after college or age XX, whichever comes first, SD21 also needs to move out.

And come to the conclusion that you shouldn't let your SDs move in under any circumstances.  If necessary, your DH could help to sub OSD's rent for a set period of time.  She's at the age where she should be living with her peers.  YSD can visit between terms but there is no reason that she shouldn't split this time with being at BM's new place.  For your piece of mind, I'd even consider subsidising her flight costs to get her across country.  

You do not need them in your house to treat you like an unpaid maid.  Your health both mental and physical will be at risk.