My Wife Is Converting Our Kids To A New Religon During Our Divorce

I'll try to leave out the dramatic details. In January of last year, my wife had an affair, and we agreed to get a divorce but remain together with our kids until we figured everything out. There's never been any yelling or physical abuse, and she says that I'm an amazing father to our kids, of which we have four. The kids are between the ages of 3 and 10. We reside in Wisconsin.

We agreed not to tell them about the affair and to not introduce new partners to them if she or I met someone until long after the divorce. She apparently left her affair partner shortly after and began seeing the father of one of our kid's friends. At this point, the kids did not know about the divorce.

We decided in April to tell them about the divorce (lots to figure out financially because I was the breadwinner). That Friday, she took the kids with her boyfriend to a bunch of family activities without telling me. She said that she wasn't beholden to our agreement and would do whatever she wanted. The kids figured out very quickly that they were dating. Since then, they've seen this man an average of twice per week, always while I was at work. It's been very heartbreaking. Everyone I've asked has said that there's nothing I can legally do to prevent him from spending time with my kids.

We have been in the process of a mediated divorce because of our low income. We no longer live together and have been doing a 50/50 custody schedule. We finished negotiating our settlement agreement, and the court date is set for mid-February.

This week, I've learned that my ex has been secretly taking our kids to Catholic church and putting them in religious classes. This is her boyfriend's church. My ex and I were both raised Evangelical/Lutheran and have no Catholic friends or family. I disagree heavily with this but have not said so yet. Our marriage settlement agreement very clearly prohibits unilaterally changing their religious upbringing, but it's obviously not official yet. I'm sure this also violates our mediation agreement, but I haven't had time to look it up.

I feel that she doesn't have the right to convert our kids in order to appease her boyfriend. I don't want to rock the boat while we are so close to finalizing the divorce. Is there anything I can do to halt what she is doing? If I should wait until after the divorce, what steps do I take to enforce the agreement?