The one pitfall I'd like to mention when registering your own attorneyship with the bank is that while they usually accept there can be more than one attorney, often they only want to have to deal with one person. They want one address to send bank statements to, and one person to have a debit card and/or cheque book for the account. If this is the case and they consider having done their duty with your brother, then all you could realistically do is set up Internet banking that could in theory be shared with your brother.
My daughter and I have registered poa with dads bank and we both have cards and statements sent to us and can both register for online banking on his account