SE doesnt Ban people using IP's or Mac address's simply because its to easy to get around it
They do however ban Credit Card Numbers, User/Pol ID's and if your banned too many times they keep your personal information (address, name, email things that you enter when making the account and setting up billing) and if you try to make a new account it gets rejected
As for Mac Address, if any every Bans a mac address on PC or PS2 (i know Socom did this on PS2) you do not need to buy a whole new system just a new NIC (Network Interface Card, pc) or Network Adpter(ps2)
and for the OP, if you dont want your "Brother" to get you banned again, do not set POL to log in Auto, and put a Member Password on it, will mean he would have to crack your POL password and the Member Password before he could even get to POL