MIL forcing our children to go to church

So me and my husband are not very religious. We also aren’t against the idea of God we just choose to not go to church for personal reasons. Neither of us were raised in a religious home and didn’t grow up going to church. His mother recently became very religious after marrying her new husband. All of a sudden every thing she does “is because god wants her too”. Whether it’s good things or bad things but that’s another story.

She told us our kids have to go to church every Sunday so they can go to heaven ( she already told us we are going to hell because we don’t go to church)..

we are pregnant with our first child and we will let that child choose what they want to do when they are old enough. But she says she will be taking our child every Sunday to go to church and we have no choice. She also says if we don’t let her then our child will not be allowed to celebrate Christmas and she won’t get them Christmas presents because that’s a religious holiday and you have to be religious and go to church to celebrate it.

I am so frustrated by her and can’t stand her she says she is religious. But she treats everyone like shit except her new husband.

Me and my husband can’t stand her and would never feel comfortable leaving our child alone with her anyway. ( not because of the church thing but because of all the crazy nutjob things she does and overall we both agree she is a terrible person)..

what would you do in this situation because I already know she will try and make our life’s hell if we don’t give in to her.