Hi Deckswabber, just read the thread, I am going through similar but no poa registered. Joint Poa is tricky and it should have been thought through before, if you knew how things would be you shouldn't have committed yourself really, but while you are you will have to meet with your brother. You do need to talk, regardless. It should be you and him and a solicitor and you will have to go into it with some strategy.
One option might be for one of you to be removed from poa. Don't resist his solicitor because whoever he is will be bound by rules and will be impartial, If DB behaves like an idiot then the solicitor will see that.
You haven't said much about the move but if it happened against the rest of the family's wishes then you would have known the consequences of that, you are just going to have to accept their behaviour, unreasonable though it seems, but if you moved her surely you had DBs agreement?
Regarding the stuff at Auntie's, do you really want it? Consider whether it would be better to let go of it or ask for a few items and he can sort out storage. Auntie will soon get fed up with it.
It might be better to divide responsibilities, with a lawyer present so you can each get on with different things. It might be easier for you to let go of POA entirely, then all you have to do is visit Mum and he can do all the paperwork and take all the responsibilities.
Having POA is not about having control, it's about doing what is best for the person according to their wishes. After death everything that you both have said, any money being spent is held up to scrutiny so if he plays silly buggers now, legally it can be resolved later.
I think you should let go really, at least you can hold your head up and get a bit of peace of mind. If you withdraw from the scene they will probably start squabbling with each other, leave them to it!
I have not mentioned the familial bullying etc, as it may resolve itself, a bereavement or change like this reshuffles relationships completely anyway.
It might be that if you let go he will actually not want the responsibility and end up handing everything over. As the son he will feel under pressure to be seen to be taking charge and you might just have to allow him this indulgence to his ego in order to keep your own sanity and be the bigger person. Over time others will see the truth of what's happened.