Unfortunately you have no real control over that. It is part of the downside of breaking up.

When I left my children's birth mother, I lucked out in a sense. She never had any interest in the kids and so I didn't have to deal with whatever her life might devolve into or whatever dipshit she might have gotten involved with later. But I've encountered literally no one else who hasn't had to cope with stuff like this. I guess most people at least have the good sense not to marry someone who is mentally ill like I did, lol.

Anyway I feel your pain because I worked through it with my current wife and her kids and her ex. It's a hopeless feeling and a regrettable opportunity to practice letting go of what you can't influence.

If they can't think for themselves at that age, theres no hope. Honestly, their mom trying to thought-police them, because of their dad, is f--- ed up. Sorry to be blunt.

Unless he is trying to influence your (adult) boys to follow suit there’s nothing you can do about it, and even then it’s debatable, because adult children are entitled to decide for themselves what to do. He’s made this decision I’m afraid and that must be respected. It cuts both ways, because we often complain about our religious families trying to influence our decisions when we say we have stopped believing, this is just the same, but in reverse. It would be interesting though, to understand how he came about this change in his beliefs.

Adults make their own decisions

Well they're grown ups. Hopefully they'll see it for what it is. Some sort of desperate foray into whatever this is.

Have you found out what brought this on? That would seem to be important.

Maybe have a talk with the boys.

And they're adults. You run the risk of alienating them if you try to interfere.