WoW I have to say, it seems to me you and your husband have to take responsibility within this situation. You are the parents, you have to make the decisions. And you have to be considerate of others, starting from your own other children and continuing with the neighbourhood and with those considering a shidduch with your family in the future.
Your son would not approve of you speaking with the rabbi? Do you need his approval? And why being expelled from yeshiva is suddendly such a terrible deterrent? I thought he was not interested in that lifestyle.