You need to think long and hard. Do you otherwise have a good relationship with your dh? Is this who you want and what you want?
You cannot change his dm. She is probably lonely, feeling let down by her dp, perhaps she has too close a relationship with alcohol? Or perhaps your dh has told her something she can't abide. Who knows.
Your dh is sitting between a rock and a hard place.
But he should not gossip to his mother, his loyalty should be with you and the dc.
IF you decide you want your marriage to work, I think you should agree your dh can see his dm on his own. Your dc should not have any contact with her, no presents or cards to any of them, let alone visits.
If this compromise works for your dh and you, you better realize you can never tell him anything you wouldn't like thrown in your face
. Shouldn't be like that in a marriage but at least you will know where you stand. Please get some therapy for you if this is what you decide.
And if you decide to leave, be prepared your mil will have more access to your dd and will fight you alongside her son.
It really all depends on your feelings towards your dh and if you can forgive him and trust him in the future.