I, Your mlcer is still very much into himself. He's not ready to have any kind of relationship w/his children, but when he does, he will most likely choose the one that will not question his actions. Which child is easier to manipulate?
Yes, he is like a stranger to them. Heck he's a stranger to everyone who knew him previously. After all, he's acting out and is most likely the same person he was as a boy, long before you knew him. Your children do not know how to relate to him because they are still "seeing" him as their father and not someone totally different. Once they understand that he's different in every way, then they may be able to relate to him....but a lot will depend upon him contacting them. Your children are not stupid and know that what he's doing isn't right.
BTW, don't worry too much about the no contact. When he needs something, he'll contact you. I've not seen one who hasn't needed something along the way.
Take care.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.