I resorted to cutting off a couple relatives after trying vainly for several years to get them to respect some basic boundaries which they repeatedly ignored. I'm talking major stuff, like your stuff is major.

I cut them off when they started aiming themselves at the children of the family. When it was just me, I felt strong enough to stand up to them, even if it was annoying. But kids are impressionable, especially teenagers, and it's our jobs to protect them from the members of our families who could pose a danger to them.

Your cult-affiliated family members pose a danger to your children because they've repeatedly shown they're willing to try to indoctrinate them whenever your back is turned. Do whatever you have to do with a completely clear conscience.

I wish you the best.

P.S. I still care about the relatives I cut out of my life. I'm not even angry at them. I just don't trust them for realistic reasons.