I'll tell you how I handled it.
In my marriage, my mother in law was a ruthless c-word. She was judgmental, mean-spirited, controlling, abusive, and arrogant.
If she didn't get her way, she'd blame her grandmother's insanity, her mother's suicide, her dad's untimely death, her stint in a Catholic orphanage, and my father-in-law for everything that was wrong in this world.
Enter me. Once the engagement was announced, she would criticize me for everything I did. It didn't matter what. She'd complain I didn't go up to Kentucky and work on their farm, for free, for the summer -- as if I had the financial ability to just quit my job. She'd excoriate me in front of my wife, and try and humiliate me in front of other family members.
You know what? I ignored her. With the wedding she had to have the final say on everything. So I paid for the wedding and took it all away from her. The more she complained the more I ignored her.
Eventually she was bitter. So much so that it was totally irrational. Even my father-in-law would have to take her to the mat on some of the crap that came out of her mouth.
Soon she simply stopped communicating. I was fine by that. And as she got older she realized she'd p*ssed off enough family members that she'd try and buy their affections back, only to lash out at them and dredge up past slights from decades before.
Some people are unhappy. They can never be pleased. So your husband better just man-up to the fact that his mom is a controlling, manipulating person.
Finally, he married you. That means he agreed to stand tall for you whether you're right or wrong. Its that simple. If he can't do that then he's failed you.
Heck just tell him you want a divorce because of his mom and his ball-less inability to defend his family from her tirades.
Eventually he's going to have to stand tall or move in with his mom and he can be visiting daddy from now on.
I doubt he'd sacrifice his family just to let his mom "win" in this ridiculous, silly and outrageous war.
There. I hope that helps.