How old/big are you compared to him? I always managed to convince my brother of my way of thinking one way or another... :D (Threats of violence)

Maybe talking like you might kick him out of the band would be enough to freak him into coming around?

Bands are often like this and famous bands with siblings quite often have their problems on top. What happens if when he's saying 'I'm the best drummer in the world man, bow before me'.... you just come back with 'yeah, you are the best drummer in the world... now lets get on with this'... ?