Zahavasdad, no you can’t separate the kids in this, WOW said one of his chevrah came to help the younger son. This is a group issue with both sets of kids and they all have to be in this discussion of what to do and how to go about it. It is a lesson for all of them and maybe and opportunity they all need to undo or heal some of the issues of the past!
What would you have said to your “bully” if you had the opportunity? What do you want to say to this one? Let everyone write their own letter to him. They have all learned Torah in the past. They are NOT amharatzim. They can still look things up and bring examples. They can sit with your husband and find the examples they are looking for. Your oldest certainly knows how and where to find them. This is a very productive way of teaching this Talmid Chochom a lesson and allowing all these kids to do something productive and positive with their pain!