My issue would be with your son.
I can't comment on your son, since I don't know him, and you quite obviously know him best.
I do feel that I can throw some light on how the teachers feel, since I teach in a state comp myself.
Teaching is largly done bythe common consent of all the people in the classroom. All the kids know that staff have very few, if any, real sanctions that they can use in the case of bad behaviour.
Being able to teach effectivly involves being able to mannage a classroom efficiently. And for that to happen two things must be in place. The kids must have a degree of respect for the staff (and vica versa) and the staff must have 'presence' in the classroom. The Senior managment must be seen to be supportive of the classroom teachers.
The situtaion that you son now finds himself wrecks both of these. Due to his actions the teacher will now have zero respect from the class members. She will be seen as a joke. Because the governers have returned your son to the school the kids will have been sent a strong message that they do not support the teacher, further undermining her position in the classroom. This will effecivly make her position impossible within that school.
I realise that kids can do stupid things, not out of malice (although that does happen). However I don not feel that you son returning to the school is the right decision.
It isn't that I think that your son is irredemably bad, or wicked, but I do feel that he has put this teacher in an impossible position.
I am sure that other schools would take him. That way he can have a fresh start.
Your other children didn't do anything and shouldn't be moved, unless that is your choice.
I hope that things get sorted out soon.