I think you are the lady who posted about the 14 & 15yo boys having to do childcare for their mother?  If that's the case, then if your DH goes to court and gets some defined visitation, like every other weekend, then once that starts happening, you guys could make daily showers part of the routine at Dad's house.

This would be something Dad, not you, would start with them.  He could also buy deodorant and whatever else was necessary in the hygiene line ( toothbrush, toothpaste, floss, etc.)   He might encourage (or turn a blind eye to) the boy taking his hygiene things to Mom's, it would be a good thing and you could replace so there would be stuff at both places, in other words, no excuses not to use them.

Good luck!

If the kid hasn't had good training about how to take care of himself, or he's not been held to any standards then it's not surprising he behaves like this. Kids don't often spontaneously decide to care for themselves, they usually need to be taught how to behave. So likely part or most of it is poor parental training. 
That said, teen boys do tend to be kind of gross and i do have nag mine sometimes that he needs to step it up. It's probably a two part problem but ultimately it's on the parent to teach them how care for themselves and hold them accountable if they don't. 

Kids who have been raised with hygiene standards from a young age usually do not need reminding or need to be told to bathe. Unfortunately here, it's standardly problematic.

I told DH that YSD15 stunk up my car on the way home the other day, I had to partially roll the window down (Yes, coming from BMs).  She showers about every 2 - 3 days but I told  him it's now got to be, GOT to be, every day.  But that's just me talking into a wall.  So basically no more rides with me (this is very, very rare anyway) and no sitting near her (also rare).

My SD13 needs to be told to bathe... not sure if it will improve once we start socializing more now COVID rules are relaxing and school with be back to in person. 

My theroy is that it is just not part of her routine (there is very little routine going on in our house which is a whole other issue) and she has unrestricted access to the internet and electronic devices which are highly addictive and difficult for her to drag herself away from unless she is told to do a thing right now. 

The stink has gotten better compaired to last summer after we realized that she was not changing her underwear very frequently and had worn the same bra for months on end (even in bed). So we got her more bras, more underwear and try to remind her that changing clothes and unerwear is important. I am still not convinced she changes underwear every day but the stink is a lot less than last year. 

To add to this. I am increasingly becoming convinced that my SD's life experiences (including the divorce, having had young parents, moving around a lot and her mother being her mother) that her maturity is just not where most kid's maturity is at her age. From reading here I think that many of these kids are in a similar position where their maturity levels have been stunted by divorce and sub-par parents. 

My ss's barely shower, and one doesn't change his clothes. I've complained to no end and have just resulted to calling him Linus from Peanuts, I can just see the stink lines wofting above him.. They are going to have to live down being the greasy smelly people among their peers, not me. My younger kids are toddlers and bath every 1-2 days and ask for it.