OP - don't lose sight of the fact that your children will have your values, that you are authentic and the core of their lives are with you. I'm afraid you do have to build some resilience to this.
You have to accept that he will do things differently, and they won't have the same quality of care as they receive with you.
But, they will be safe and they will be looked after.
DC4 (9) will come back having not showered, not cleaned her teeth. She goes for one night a month with her siblings. And has nothing much to do with him outside of this. He doesn't engage or attempt to get to know her. The others go more often - individually - once a week. I hate it, but it's their choice. To me they are pandering to him. They do nothing, save play on gadgets and eat crap food. Even when they are all there, He will go out - does what he wants to do, with DS2 who is his favourite.
I have had to accept XH is how he is. Narcisstic, possibly personality disorder (I encourage you to read Walking on Eggshells). The only thing I can do is instill my values, our family values, and show them really good care and attention.
All I can say is minimise the contact, encourage them to go. You have to support them in this. They will always come back to you.
It's horrible, my heart goes out to you.