My guess: your husband thinks the issue is the food. You may need to explain things to him -- that you don't feel welcome. This isn't about making him choose between families -- it's about your kids and their memories about Thanksgiving ( They're not getting the same warm feelings he was as a kid, they're seeing their mom being left out)
I'm wondering-- does your husband want to go, because-- as dysfunctional as the day feels for you-- for him this is what a "family holiday" is and he wants to share it with his kids?
Or is he afraid his mom is going to give him hell if he backs out?
This year it is a little late to cancel... if I were you I'd have your family b-day cake with friends over the weekend, and let your MIL have her Thanksgiving as she likes it. Sit down and smile and just grin & bear it.
But it looks like a big talk is in order to come to a new agreement-- whatever his reasons, he has to understand it's not fair that you have to spend every Thanksgiving, what is supposed to be a nice holiday, somewhere that makes you feel unwelcome and awful.
Maybe alternate years so he gets his family one year and you get to plan something else the other year. Let them know WELL ahead of time that you won't be there on T-day... don't wait until November.
Either that or, if he doesn't like his family T-day either and he's just going to appease his parents, maybe you can convince him that your family needs to start your own T-day traditions at home, and his parents are going to have to deal with it.
Or at least agree to him giving you a free pass like your sister in law and start spending the holidays apart.