I think a family meeting is in order here. Firstly, your wife is supposed to support and respect you, however, as its her daughter and grand child its not easy.

What these two youngsters must take into consideration is that they are merely guests in YOUR home, give them a time limit on how long they can stay with you and stick to it!! The longer you leave it the more of a mess it becomes. Are they contributing financially at all?? If not, you are being taken advantage of!! The same has happened to me a couple of times and i vow never to let people come and stay again unless they are aware of the rules and regs!! All the very best.