OP, I don’t know if you are still reading but I have a few thoughts about dealing with this (pending lawyer approval). Get a second opinion, especially from a law organization that is fighting against these unconstitutional no-fault divorce laws.
-Get on record that together you made decisions about marriage, children, faith and raising your family. Now that your husband wants out, he alone gets to decide these things (or if you don’t agree with what he wants he alone decided to give decision making to the judge.
-Ask for more than half custody. You have been with them from birth (in whatever capacity for your family - homemaker, always put them to bed?) and having them away even half of the week is not fair to you or (more importantly) them. Always remember that custody agreements can change.
-Try to get in the custody agreement that they will not spend the night with a non family member without approval from the other parent. This will be difficult - especially as they want sleepovers with friends, but I think you can see the benefit.
-Live the joy of our Catholic faith! Show them God’s love! Pray with them, for them and for their Dad.
-Teach them the fullness of our faith. Read the Bible. Start them memorizing the Baltimore Catechism. (Start with the first with both. Move to 2nd when they are older and can understand the commentary.)
-Teach them to love their father even as they learn that he has chosen this life (and even sacrificed their happiness and well-being for it). Remind them that he is their father and that they need to always show respect.
-The respect thing is huge - especially since he is doing NOTHING respectful. At any time, he can go back to the judge and ask for more custody or a different agreement. This is why it is so important to get on record that in leaving the family, he gets to call ALL the shots. And why you need to be all loving, forgiving and respectful.
May God bless you as you try to honor Him, your marriage and husband, and his children by raising them in the faith you both professed for them.