M.W.
Oh boy...what a mess. I am fortunate to have 2 MILs...YES 2. My husband's mother and his stepmother. His mom and I get along but she would always say things around my family when neither hubby and I were in the room. She also felt that since she treated my family like her family, they should do the same. Therefore, I couldn't go to my family's for thanksgiving w/o her, her brother and my BIL. This used to really piss my family off becuase they knew they had to tolerate her out of love for me & hubby. It took awhile to get hubby to realize that no one we knew traveled with their inlaws!
My suggestion is go and have dinner and then depart early. Not in a way that you appear to eat & run. But perhaps plan to take the kids to see Madagascar or something at the movies following dinner. They may not like this but if they don't talk anyway, what should it matter. At least you won't have to deal with the tension!
Hope this helps.
M