@c730127b
It sounds like to me from your post that even though you (and your brother) have POA, Durable, I hope, that your mom's financial institutions didn't have it on file for activation. This could have been handled prior to the current situation. IOW, all the checks and balances could have occurred before the current situation.
NOLO: Durable Financial Power of Attorney - How It Works
Places that have our money have to abide by our wishes and legal documents especially in this day and age when there is so much identity theft - but those legal documents have to be checked for truthfulness, timeliness and accuracy.
Credit card bills or any other bills should be easy to change - just send in a change of address and to keep it simple for you the new address should read: Her Name, c/o Your Name, POA, Your Address.
By changing your mom's address to your address, you are in essence making your address her place of legal residence. So the good thing about this is once you get it all changed over - it is done.
For financial institutions, since they evidently didn't have the POA on file, you will have to go to each one or if not local, contact them, as you have done and complete the whatever paperwork they require. Take the original signed and withnessed POA giving you power over her accounts guess a copy will do if you have to send it - if your brother is also co-POA holder, then yes, you have to have a legal document from him that you are acting for the both of you.
For Social Security benefits management for your mother, you will need to be a Social Security Representative Payee - Social Security Administration.gov - Representative Payee
You can follow this link on SS Representative Payee and it will describe what you have to do.
You will need authorization for managing her Health and Medicare benefits too unless she already has this set up. Medicare Authorization for Release of Health Info The Social Security office maybe able to handle this too - ask them.
It's Always Something . . . . Roseanna Roseannadanna