I hate to admit it but that really sounds like the only option open to you. Your house is to small to have 2, 3 week visitors even without the cat issue involved. You all will be tripping all over one another and I agree, your cats should not have to be punished because you have company in the house that can't respect them. Three weeks of that is a disaster waiting to happen and I strongly suspect that it would not last 3 weeks and end on a very sour note.