I agree let the g/f and brother handle a lot of it, let them tell him its cool when rolls get botched, its part of the fun.
I think that part should be empathized is that when things go south the experience is enhanced for everyone around the table and that he is cheating them of the true experience.
As far as what to do in game to bring balance? That is a hard call my friend.
You could just let it go, everyone is their to have fun first and foremost. This would be my choice.
That being said a little karma being handed out via story isn't to bad as long as it doesn't take away from everyone having fun.