You are completely in the right!
You have a small home with one bathroom, several pets, etc... And, they think they can just waltz in.
They are considering making a move, so they think it is okay to give up the roof over their heads and take advantage???
You do not need to enable this any further.
Your son is big enough to loose the pull-ups, put on his boxers, and make the necessary arrangements to provide for him and his wife and 'family'.
I would not take them back in.
I know as a parent, that this is very hard to do.
But, he is a married adult now.
You are not, and can not be, responsible for him.
