YSR>
1. Family law sucks. It's unpredictable, expensive, and judges tend to just rule by the seat of their pants.
2. Generally a judge will take the best interests of the children into account, so doing something like trying to prevent them from going to their mom's wedding shouldn't be looked on too kindly.
3. The mom was stupid to schedule a wedding for a weekend when she didn't have the kids. She also could probably have called it vacation and given 30 days notice and would have been able to do it. I'm guessing--and only guessing-- based on a strict reading of the custody order she's technically in the wrong here and the ex is going to make this hell because of it.
4. The first judge that says one week on/one week off is disruptive is pretty silly. That's probably the second most typical custody arrangement.
With all that, she needs to get her lawyer to ask for an emergency hearing, or negotiate with the ex to let him see the kids more, which is what he's really leveraging for.