He's such a jerk.
I don't think it unusual for a divorced parent to call their child nightly. Most reasonable parent would observe when the child is busy, or has a late game, and send a text "night I love you" and not call repeatedly like a psycho.
I think if you try to set up a weekly date you are going to open a can of worms. The divorce decree states he can call their phones when he wants too. He shouldn't be calling your phone at ALL - so perhaps send him an email copy and paste the section of the divorce decree that says he is to call their phone highlighted or in BOLD. What I am unsure of is if they are supposed to speak to him nightly - you don't write that was mandated - I am thinking there is no requirement.
I'm sorry the kids have to feel obligated to speak with him when they are busy.
If he has SUCH an ISSUE with it I guess he can go back to Court, and whine to the Judge. Your ex is a real life walking a talking Shingles outbreak.
I so wish he would decide to "find himself" and move to Timbuktu.