They don't have any real 'power' to do anything. What do you fear? That they could cut him off from his friends or his mom? Yes, probably, they will try to do that. And they have a good chance of succeeding, too.
All over these boards are the stories of people who have survived this crap and are so much the better for it. Shame on them for haggling with a young teen-ager. BUT THAT'S WHAT THEY DO!!! He's not the first and until we make more headway, he won't be the last, either.
Get him some copies of the books people have written about leaving and he can count his blessings that he's so young and able to do this before he's wasted his whole life.
Hurrah for your wife for taking a stand and allowing her God-given maternal instincts to kick in. Let her know how much you appreciate this. Lots of witnesses do manage to walk that double line, being true to themselves and still doing the witness performance thing.
Some people who have been harrassed about leaving have gone as far as to take out a legal injunction against the witnesses to force them to leave them alone.
It works, I hear.
Good luck. Have I mentioned how lucky he is to have you?
He won't be 'underage' forever. Four more years and he can say and enforce whatever he wants. It's his life now but it will really be his life then.
Stick by him.