Should I cut my son off and his mother‘s whole side of the family?

My wife and I took my first grandson in straight from the NICU because Dcyf took custody from my son and his girlfriend before they could even bring him home. We had never met my son’s girlfriend, until after my grandson was born for the first three months of my grandson‘s life. We were only able to visit him once in the hospital because my son and his girlfriend claimed scheduling issues come to find out my son has only visited him twice in the three months that he was in the hospital his girlfriend maybe one time or that my wife and I didn’t know any of this until my ex (my son’s mother) called me one day in a panic saying that the state was taking custody of my grandson and putting him in foster care. My wife and I had no idea until that day that there was anything wrong because as we were being told from everybody, my son, his girlfriend, my son‘s mother that the baby was doing great. Come to find out. He was not doing great. He had a lot of medical issues and nobody was visiting him in the hospital.
My wife and I talked long and hard and reached out to Dcyf find out what we could do so that my grandson would not have to go up to foster care a week later my wife and I took my grandson home from the hospital and he has been living with us ever since that has been four months. In all that time, my son has not called to check on him. Come over for visitation. Responded to Dcyf or done anything. My son‘s mother and her entire family have not reached out at all no visitation or anything. The only time I hear from my son or his mother is if I send a picture of my grandson. The only response we get is a short reply of how cute he is.
My grandson now a little over six months old, really only about 3 to 4 months because he was a preemie and born way too early, is thriving! He has overcome almost all his medical issues! He is in a loving home with my wife and I go out of our way to do everything we possibly can for him. He is a very happy baby. I guess why it hurts me the most right now is that nobody from my son‘s mother side of the family want anything to do with this beautiful child and it is shocking to me that my own son could write off his son like he did not even exist
Again, we have made several attempts to reach out and set up visitation for anybody who wanted to come over, but with the lack of interest I’m starting to wonder if I should give them the same amount of interest as they are giving my grandson