I think a trip where you have a hotel room and they have a hotel room gives you many more "outs" than them living in your place. Anyway - just a suggestion if the worst comes to pass. It does sound like you have a culture issue here (one of your husbands family's culture vs your own!). You have to be true to yourself. You are NOT going to build up a good relationship with these folks if all you are thinking when you are with them is "get them outta here!". You have to be honest about this with your husband first, and then them. Perhaps writing it all down might help. Explain your background. Explain how you already feel claustrophobic in your own home (exaggerate if necessary!) and that more people in it would be really hard for you. Put it in terms that explain "I would feel trapped"; "I would not like it" rather than "you are causing a problem" - so that they understand this is about YOUR feelings not anything about them.
Good luck anyway. I have 2000 sq ft but I still hate having my MIL to stay! Even my own family, when I visit UK, I NEVER stay for more than 3 days. First day is great to see them. Second day is catching up. Third day is planning to leave. Never over-stay - it destroys relationships!