NannyOne The boy is 22 he will be gone soon, can't your daughter wait.
IMHO in these instances the children/Young Adult's in their own home, should come first, having her boyfriend move in would mean her son would have to move out, that can not be right.
The fact that he does not like him and has had to put up with him for the past four years is enough.
I appreciate it must have gotten lonely for your daughter and she deserves a massive pat on the back for doing so well but her sons needs should come first.
Why does he need to move in right now, I am sure they can wait.
I am positive not a lot of people will agree with me but it is my opinion