Judy, I have the same problem.
I have divorced my xNPh many years ago. He didn't bother with our children, and my son had the hardest time of it. He had no use for his father. Him and I had a very good relationship.
Then he met this young woman. I have not met her until she was pregnant with my grandchild. They got married at age 21, and I was in 7th heaven about the baby. We drove 2000 miles to be there for the birth, after which she wouldn't let me hold the baby... After that, it went much worst. She was a spoiled NP, only child. We were expected to lavish as much stuff on them as her parents. Her parents had one child, we had 6.
Slowly but surely she has brainwashed my son. We were not allowed access to their children, couldn't take them to the playground even. We kept sending presents to them, never did they acknowledge that they got it, let alone thank us. Then slowly, but surely, all contact died. For years the only contact was us sending presents. We decided enough is enough. They live 5-6 miles from us, and I haven't seen them in over 7 years. I wouldn't recognise my grandchildren. My daughter has been rejected also. She has not made the choice of rejecting us, so they rejected her. DIL is into total control. I think my son might have inherited my xNPH's disorder to some degree. I also think that he suffers from the Stockholm syndrome.
I have learned to cope with the situation. I don't even want him back, I would never trust him emotionaly. He is 43, if he hasn't found his backbone yet, he never will. I'm 71, and I don't need any more pain in my life. I don't want him at my funeral, and since I don't have a son, I wouldn't go to his.
Dolly