If the issue is how is he affecting the other siblings, this is a new separate issue. I have seen where one other sibling is affected in some way although you don’t know if that would have happened anyway. But if you think that the others are being affected, this is your call, would you be willing to sacrific so to speak the first son, for the sake of the others. THis means throwing him out but I wouldn’t do that but would offer him a program that he can board at. But its your call, how important is frumkeit for you regarding the other children.
My heart breaks for you. I think I would draw the line at public CHilull Shabbos. since he shares a room then he can’t do anything there, in the bathroom he can listen to the ipod. I do think he can influence the other children negatively in the sense of following your Derech. It does seem that he does not feel like he has to listen to anything you say so maybe the tough love time has come.
Prior to this move, I would ask you if you have gone for family counseling yet with him. this would be helpful.
I also would be interested approx. how old he was when you moved to EY this can cause alot of problems for youth, I am speaking from personal experience. If they dont’ make friends in the new community, as happened with me, then I started to feel an abandonment of parents love, i.e. why they did this to me.
this sort of feeling if he has it might come up in therapy and could be road back at least for a better relationship.