My sister just recently purchased a home with her fiance. His father is wanting to move in because he is unable to manage his life. The fiance says it will only be for 2 weeks (but this is not believed by anyone). If he moves in, can my sister say he has to leave after 2 weeks, or does a contract or some sort of agreement have to be signed? She is afraid since the house is in her AND her fiance's name....that he can say his father can live there whether she says no or not.