A real shame that your Dad has let his wife control his life regarding his interaction with his son. I certainly would not stay with a woman who acted that way.My parents are only part of it. Losing our daughter at 14 (after nearly losing her at 9) took its toll too.
Mrs AFB mother passed away in her 50’s. Her Dad is a waste of space. Not heard from him in 17 years or so.
Then my Dad’s wife doesn’t let us in the house. Doesn’t let me even see my Dad really. He only talks to me on the phone if she’s out or he is.
Then we don’t talk to my Mums husband for reasons I’ll not go into here.
There isn’t any extended family that I’ve seen or talked to in decades.
So yes I’d say cursed is the correct term.
It seems it is similar with your mom. Although you have no use for her husband, it appears she has not for whatever reasons made the effort to maintain a relationship with you without involving her husband.
Very sad and unfortunate.