What an awful situation. I think Billy's suggestions are good ones.
What worries me is that my brother had been living a pretty happy and balanced life, and now all of this .
His parents, with their new fanaticism, may be storing up trouble for themselves anyway, then. He's 10; he'll soon hit his teen years; he'll have strong memories of the 'happy and balanced life' to compare with the new dubbie life suddenly thrust upon him. Just be there for him when you can - he'll need you.