She sounds horrid! Controlling and manipulative. Poor you.
It's going to take time for him to learn a different way of relating to her, but he is going to have to learn somehow. You say your relationship is otherwise good; I suggest as a first step sitting calmly and trying to get him to agree that the current situation is not working.
Then agree some basic parameters. You might have to concede some ground but so must hex make it clear that if he isn't willing to address this you are not sure if you have a strong future together.
When you are with her (and try and minimise that, twice a week is MADNESS), I would put together a rotating script that always ends the same, like this:
"Well that's an idea, but....
Interesting thought, but...
Thanks for the suggestion, but...
Gosh that sounds lovely, but...
... we're going to stick to the plan we agreed."
If he isn't able to say it too (he's got to get there at some point but I appreciate these things take time and you need help now)- perhaps he could agree to at least nod and hold your hand as a sign of his allegiance?
Say a version of it over and over again, every time. Perfectly pleasantly but firmly. Imagine yourself as an actress playing a part in a play. Make it a comedy in your head if it helps, Meet The Parents style.
You might also practice "Oh Linda, I don't think we need to worry about that" with a sympathetic head tilt that suggests you think she's acting badly for her more rude comments such as your wedding being a sham or whatever it was. Pretend you're dealing with a aged and confused relative in your head if it helps. Sympathetic but firm bemusement.
Good luck! Keep us posted.