What a tragic situation! Your husband’s actions may have caused your son to develop a paraphilia called erotic asphyxia. Sexual arousal is heightened by cutting off oxygen to the brain. It’s a dangerous practice because people sometimes wait too long to give themselves air and then suffocate. Some teens stop doing this when they realize the risks. Others don’t and develop a lifelong compulsion.
I hesitate to comment on the counselors’ approach with your daughter since I know so little about the case. Generally, however, I don’t think it’s important that abuse survivors remember every incident in order to heal. Further, hypnosis sometimes yields “false positives.” To my thinking, your daughter remembers quite enough. She knows she both witnessed abuse and was herself abused and scared. She is getting support for her feelings and, hopefully, she is learning to manage them so she no longer hurts herself.
What complicates an already painful situation is that your daughter isn’t the only victim. It’s important to remember that you and your son are victims too. Your husband’s idea of discipline was to make your son believe he was drowning and to threaten more of the same. You are also a victim of that incident. You are feeling terrible that you didn’t see what was going on at the time and now feel torn between the two adult children you love.
For these reasons, I think this is a family case. I think it would help all three of you to see a family therapist to help you acknowledge the pain of that chapter in your lives and to have a place to work through the feelings of anger, guilt, betrayal, and fear that now get in the way of your relationships with each other. My guess is that you all have unresolved feelings about your husband/their father as well.
As for whether your son’s children are at risk: The only way to know is to ask your son. Sometimes abused kids work extra hard to be sure that their own children never suffer as they did. Sadly, others repeat what was done to them, partly because normalizing the behavior of the abuser is the way they make some kind of sense about what happened to them. This is yet another issue that could be addressed in family therapy.
Your daughter’s counselors, of course, have had the opportunity to get to know your daughter. I’m limited to the information I have in your letter. I therefore encourage you and your daughter to talk with her counselors about what they think about expanding her treatment to include some family work.
I wish you well.