Yes, I would agree that what you describes sounds abusive and potentially emotionally and/or psychologically damaging to the child. But it sounds like you already knew this based on your own instinct and also on the testimony and opinions of other children and therapists. Do you feel that the child is being helped by therapy?
I'm sorry for the delay in getting back to you.
Yes, based on what you've said about what their visits are like, it seems totally reasonable to request supervised visits- at a minimum. Would it be possible to stop visits entirely based on what's going on? I would think that the child's therapist could testify to this and also perhaps the other children involved might be willing to come forward on his behalf as well.
I would strongly encourage you to continue taking the child to therapy- treatment of abused children is often long, slow and painful work but very important to do in order to help him to not only feel happier and safer now but to preempt all kinds of relationship problems in his adult life.