I am a divorced NCP of three kids. My ex gets a huge CS check each month of 3k.

I don't know what an NCP is. Your children are being brainwashed by their mother. She is obviously still angry and bitter and resentful of the divorce. And she will use this to manipulate your children. Consider this: you can now be free to live your life, see your children, be a father, and seek your own happiness. You can live as you please with no stress about living with her and all the problems. You can eventually, when you get over your present state of mind, find lovers and a partner long-term. I wish you to find a place of peace. Teach your children well. Do not speak ill of her in front of them. She should be mature enough to do this too. And move forward. I know my sister-in-law did this. Wasn't easy. But when their son was old enough, he figured out on his own what a schmuck his father was. You may even find they may turn against you. I had a dear friend on EP who experienced this as well as a friend in real life too. All their children returned to them in time. One cannot fool children forever. I wish you some peace.