You can do it but understand your accounts will be subject the strict scrutiny and constant reviews by Google. If any one of you does anything Google doesn't like then there's a good chance both accounts will be disabled.
What? Hell no, the risk is too high, I wouldn't take it but if you want to its your choice. I would just use another PC, I mean seriously, you can get a netbook for $300 bucks these days.
I've been doing this for quite awhile with no issues. I have two accounts--one is personal and the other is under my business tax id. I routinely log out of one account and into the other without a problem. Now if you are doing stuff you shouldn't be doing it probably won't help you. If your brother does something that gets him banned, it might cause you problems. Oh and getting a netbook isn't going to change aything unless you are using a different internet connection with a different IP address.
Getting another PC is not solution. if the internet connection would be same then the problem is not solved. if you are already doing it check out the result yourself and post it here. And yes, do not rub each others back! ( means do not click each other's ads )