depends, if it's a temp-ban, wait it out. if it's a perma-ban, nothing, buy a new ps3 and have your brother pay for it however he can. perma-bans are non-negotiable usually. you can call sony and see what they say, but the excuse, "my bro did it" won't get you anywhere.
if those 2 options aren't to your liking, then you should explain more on the issue. did you get the notification email from sony and what kind of ban or how long is it? what exactly was your brother doing to get the ban? we need more info to answer your question.