My first response is, like others have said, to stockpile food, water, and litter boxes---which is what we've always done.
But, I do think this is just his excuse for not going. Maybe he is too embarrassed to say that they can't afford it. and if your sister is backing him up, then she probably won't go without him.
So, it seems to me that you have two choices:
1. Take your parents and have a wonderful time without your sister's family.
2. Have a heart to heart talk with sis AND BIL--explain that you know things are tough right now, etc, but you want them to come as a GIFT from you with no strings attached, etc.
I know it would be hard given your feelings (understandably) about your BIL, but if he knows the family thinks of him as a deadbeat, etc, it's no wonder he doesn't want to come. And if your sister won't come without him, I would think you might need to work on him.
Good luck with whatever you decide!!!
