Nothing is going to change here @Sunshine231 until you accept two things :
Your MIL will hate / blame you no matter what you do. Choosing not to have better boundaries so she isn’t proved right in her nonsense, is only giving her more of what she wants. An excuse to abuse you.
Your husband is the bigger problem. The first time his mother bad mouthed you should have been the last one.
Continuously repeating the same dynamic of going round in a mood, ‘having’ to tell his mummy that you’ve had a row, constantly feeding her with information to validate her continual verbal abuse of you and doing nothing to stop it is not him trying to keep mummy happy. He is getting as much out of this as she is. Jumping to please a brother who calls you a cunt is the same.
You need to get very clear and very tough on how this situation is resolved before your children are old enough to be dragged into these malicious mind games.
Child care stops now.
Husband divulges not one detail of your relationship from now.
Every comment, snide dig, passive aggressive remark is confronted by him and told no more from now.
If he doesn’t feel he has the ability to put those boundaries in right now, he gets therapy with someone who can help
him.
If he refuses any of the above he is telling you he values his mother’s feelings and her need to abuse you over your marriage and children. His love for his mother and need to please her at all costs is not compatible with a happy loving marriage.
If you don’t hold him as accountable as your MIL you are facilitating your own abuse from this family. All that will change is you children being poisoned against you and dragged into the same dynamic as your husband.