I would:
- set a schedule in advance and rent a larger car for that week so they can join in if they want (if they don't want, they make other arrangements);
- have the kids open their present except the ones given by ILs so that they can be present to witness it;
- I would not bother telling the kids to keep their voices down on this ONE morning, because hey, it's Christmas!
- not short-order cook anything. Everyone eats what I serve, when I serve it, otherwise they're on their own.
But most importantly, I would make sure to never have the ILs on consecutive years! Go to your family, take a vacation, take a staycation, just say NO.
If she's criticizing you constantly, growing a backbone won't really make it any worse, will it? Don't be afraid to be the bad guy.