It could be considered invasion of privacy.

You are asking how illegal it is? So you already know it's not allowed, but you want to do it anyways and just want to know what kind of penalty you can expect for it??
So in other words, you basically just announced that you have the intention to commit a crime?

It could be considered a lot more if he does "screw up" the info "or worse".

It is illegal. Don't do it. Making a "fake" account is legal. You can make an account using their names and post weird stuff, and generally be a nuisance.

Depends how you do it and what you do to their accounts. For example, last year in my dorm whenever friends came over and left their facebooks logged in, other people would go in and post random crap on their walls and change their statuses and things like that. Programs like Firefox can be set to remember all logins, so that's a good way to get people's passwords and such. This method is not illegal. Actually hacking into their accounts from the outside would be both quite difficult and definitely illegal. I'm not familiar with facebook, nor with many hacking techniques, but I do know many hacks use brute force attacks, which requires hundreds of PCs that have been infected with your Trojans (the most obvious tactic is simple denial of service attacks, which involves hundreds and sometimes thousands of PCs constantly spamming a website in order to shut it down from bandwidth overload--a tactic not likely to work on something like facebook). Why did I just tell you that? So you know that directly hacking their accounts takes a lot of other crimes in order to make work. Short of aquiring their passwords through some scheme (which in itself is a grey area), there's not much you can do, except somehow work out a way to be very clever and get them back.

If you have to ask that question, you shouldn't be hacking in the first place.

k i won't do it, I just feel really bad for my brother, they are calling him a devil worshipper for listening to anthrax and megadeth, and saying he will never get a girlfriend, I just thought I would try something a little less violent, but Im just gonna have to tell the school board, thanks for the help guys!

In facebook you can drop a friend, or hide the friends you don't want to see their updates. If your brother is being bullied (bully is being a bad word today), you can always report it to Facebook. Your brother's friends may get a notice from Facebook administrators. If all else fails, just ask your brother to drop them entirely. Your brother can block the bullies from the friend list.

Any hacking (regardless of what form), is illegal. How severely you are punished depends on the state you live in.

Take the issue up with parents/ school officials, save any correspondence that is causing issues.

Don't try to hack anything or make matters worse. Just report the bullying, maybe it will go somewhere with it in the headlines all day every day.