Liz,
I am sorry that your axh is using your son now, they always have to have an enabler around to take care of them. (using your son as an alarm clock??, and good for him to take an uber instead of getting in the car with his drunk Dad)
My 2dd's went and spent 24 hours at axh house Christmas night. My one daughter can't stand him and is pretty stern with him. I guess he was an axx to one of his cousins on Christmas and my the daughter saw it. She called him out about it and he apologized to the cousin. Yes our children step into the spouses role once we are gone. Both my daughters told me that he didn't talk to his mother the hole day because she dropped off the kids presents at my work and didn't give them to him. So grateful that he didn't ruin my holiday like he did everyone elses.
This is out of our hands as we are not there. He could benefit from a therapist or alateen. That would be ideal if he could go to a meeting. I am sorry about manipulation that he is puting on the son, but once again there is nothing that can do but listen and give him sound advice.
Hugs my friend!!