I think that your hub and his mom's expectations are selfish ~it's you car! You have every right to stand up for yourself and set up available days & times to help your MIL get around. It does suck to depend upon others to help you get around...but you shouldn't have to switch places with her, just to make her life more enjoyable. That's ridiculous!

Perhaps they're just sort of stuck in their emotional minds, and expecting everyone to accomodate (sp?) them to ease their distress a bit. It's just unfair to you to expect you to make all of the accomodations. It sounds challenging to stand your ground, but I encourage you to continue to do so. Tough toenails, they're going to have to make changes in their worlds too. That's just the way that it is.

and Best wishes sent your way!