I have 3 teens who are with me 90% of the time. My ex and I were together a long time. We split a few years ago. All was ok until he met his fiancée. She makes up all decisions around what he does with the kids, rules when he sees them etc. One of my teens doesn’t want to stay at their home but they are insistent this carries on. Me and my ex seem to make agreements about changes in routine etc which is all fine until she gets involved and always decides the opposite. She is also really demanding with me initially turning up at my work unannounced to introduce herself, sending me emails about conversations I have had with my ex that haven’t involved her, writing his messages to me. I’m just finding her to much. What can I do?