It's time for you to step up and to loudly proclaim that your child will be raised atheist. If he or she wants to become Catholic or Anglican when he or she turns 13, fine, but no one will force their religion on your kid. That will settle the matter.

The mother of the child gets to choose since the father doesn’t care. Grandparents don’t get a say.

You're right. Religion is bullshit. The best thing to do is raise your kid independently of any religion and let them make up their own mind. Tell them both that that's what you want to do, and if they really think there's a god, they should have faith that he will guide your kid in the right direction, himself. But if you don't care, I'd side with your wife. Parent outranks grandparent in matters of child rearing, that's how it works.

You need to back up your wife. Your mother got to raise her child/ren how she wanted to, and now it’s you and your wife’s turn to raise your child how you want to. Your mother is not the parent, she should have absolutely no say whatsoever in the rearing of your child. That’s up to you and your wife. That boundary should have been established early on, but it’s better late than never.

This is the decision of the parents, not the grandparents. Your mother needs to back off and let you raise your own child the way you see fit.