Dealing with wife's narcissistic and toxic ex
My wife and her ex have been divorced for over 7 years. They have an 11 yo daughter together, and split custody 50/50. My wife filed for divorce after his multiple affairs (and an abortion with one of them) while she was pregnant with their daughter. He's very narcissistic and tries to bully her any chance he gets. Knowing that she's not going to put up much of a fight unless it's a big deal. I wouldn't say my wife is a push-over, but she doesn't like dealing with conflict.
I have a great relationship with my step-daughter, and virtually no communication wit the ex to help prevent conflict. Recently, step-daughter("SD" going forward?) has been expressing that she wants to live with us full time. The dad doesn't physically abuse her, but him and his new wife definitely verbally abuse. Asshole, stupid, idiot, etc... anything degrading they can say to make their kids feel bad for making a mistake,.... they say to them. It's the complete opposite here.
The issue we have at hand now is that my wife and ex used to coparent pretty reasonably, and now that I've come into the picture he's been extremely eratic, and I would assume jealous. From my SD's POV, the new wife is also like a little devil on his shoulder.
He's constantly trying to push his weight around (and money) when he feels like he has no control over his daughter, and more-so our household. Threatening court action if my wife doesn't stick exactly to the custody agreement (neither parent does), and then telling her he lost all respect for her and will no longer be civil. This specific example was a misunderstanding around New Years day custody. Something he agreed to initially, then got pissed about after he read the agreement (and talked to his wife) and blamed it all on my wife while assuming no responsibility.
He also just threatened to take us to court because he doesn't want us using her image for posts on social media for my photography business. Meanwhile, her pictures are posted frequently by another photographer who takes pictures at her dance studio, and she's posted online by the studio as well. His arguement was that's ok for them to do because they're established business', and this is a hobby for me.
Besides it being a BS arguement, we know what this is about. Trying to control us, bully us, and trying to deter me from bonding with his daughter. We initially had talked this out, and decided my wife was going to tell him he had to send the same cease and desist letter he sent to us to the other 2 businesses as well if he refused to stand down from his position, but she omitted that from their discussion. Yes, he sent us an email threating legal action if we posted any more photos of her, and he said he is performing "social media scans" to make sure we're abiding by his request. Instead of just speaking to us directly and having a conversation about it.
How do we keep him from trying to keep interfering in this household? How do we handle someone like him to ward him off? I don't take kindly to bullies, and I've always laid lay to prevent conflict, and to keep SD out of any crossfire, but I'm getting fed up with it. He's picking and choosing what to threaten us with only when he knows it can hurt us. It's never a conversation, it's always a threat.