I did split with my wife... . she is uBPD and possibly uNPD. We share a teen and an almost tween. At first, I was going to fight for custody. Through various things, including her lying to get a restraining order in order to gain a higher position in case I went after custody of our kids, I opted to give her what she wanted... . joint custody with 50/50.
I decided that if I fought her... . first of all, I might lose. Though they claim otherwise, it is known that the judges (especially the judge here in our town) favors women, and I knew that if she felt that threatened she would just lie, lie, lie. Furthermore, she had already begun manipulating our kids by talking to them and putting in their heads how 50/50 is the right thing. My eldest daughter just recently realized that not ALL divorces end that way. Sometimes the kids live completely with one parent, with the other getting to see them on weekends and things.
But if I won, that would be terrible too... . that would provoke her parental alienation behaviors, manipulation, lying to our kids, etc. See... . if she feels like I'm trying to "take them", then she will try to keep control. If our kids decide they don't want to be there on their own, well how can she argue about that?
So, I opted to stick close to my kids and just observe closely, hoping that it would in many ways take care of itself. And it is. Though they do go over there every other week, I wind up seeing them most of the time because my ex is too wrapped up in her own life (and, in her defense, work). I knew it would be that way. The whole "joint custody, 50/50" is about having the piece of paper for her ego, so that she doesn't have to bear the shame of "losing" them as a consequence of her ridiculous and neglectful behavior. But my kids, though they love her, dont really want to be over there. I listen. I talk to them about it. I empathize with them without bashing their mommy -I tell my eldest, "I know, honey... . mommy did those same things to me, too, and though I care about her I decided I didn't want to be around it anymore." At some point, if things continue the way that they are, they are likely going to say they don't want to be over there at all. Kids aren't dumb. They know who their strongest bond is with, they know who is really there for them, and they see things pretty clearly. My eldest tells me how "mommy is a drama queen and she never spends time with us." It hurts to hear that and to know that she's hurting, but that is their mom -nothing I can do about that. A bit too late for that!

But I do believe that my kids will appreciate how I stuck close to them while at least trying to peacefully facilitate their relationship with her. Many people have told me, and I believe it is true... . the kids 1) aren't dumb, and 2) they really do eventually pick one parent. I didn't want to interfere with that by showing visible contempt for their mother or getting drawn into arguments -my kids are very sensitive to that.
However, if I ever find out that she exposes them to anything crazy or puts them in danger, I have been documenting everything and will use it to do what I need to do. I am in a safer position, being a man, because I don't live with her and stay away from her. Plus, I can document that our relationship is a peaceful one as co-parents and that I try to facilitate their relationship with their mom. All things that are good for the kids and helpful in court, if need be. Your situation may be different, but that's where I'm at.