Product: Checking or savings account

On XX/XX/22 my mother passed away. Her largest asset is a checking account ( approx. {$50000.00} ) with Peoples United Bank XXXX XXXX XXXX XXXX, XXXX, Maine. 
I initially contacted the bank on XX/XX/22 and was told by XXXX XXXX to come in. On XX/XX/22 I was informed that the account had been set up as a XXXX XXXX Account with my brother XXXX and I as equal beneficiaries. I was told that upon my mothers death we each became owners of XXXX of the account and by showing identification and the death certificate I could withdraw my XXXX. I was told that one benefit of the XXXX XXXX was that the monies didnt have to go through probate and therefore cash would be immediately freed up and available to be applied toward paying final expenses. 
On XX/XX/22 I returned with identification, a death certificate, and an affidavit stating that the probate estate was less than {$40000.00}. It is my intent to use my XXXX of the funds to pay final expenses and then to divide the remainder between the XXXX children. However, I was now told that the bank wouldt let me withdraw my XXXX unless XXXX came into the bank and simultaneously withdrew his XXXX of the funds. 
For many years XXXX has refused to speak or deal with any of his XXXX siblings. I told XXXX it would very difficult to get him to come into a branch with me or to provide a notarized letter. Nevertheless, I texted and phoned XXXX several times to coordinate a meeting but got no response. Subsequently I received a communication from his attorney indicating that he has no intention to cooperate. On XX/XX/22 branch manager XXXX XXXX called me to say that XXXX had called them saying he wont come into the bank or sign papers that would allow me to withdraw my XXXX of the account. 
I have asked the bank several times to see documentation spelling out their policy of requiring simultaneous withdrawals, or any paperwork my mother maXXXX have signed that would have set up these limits, but I was told I couldnt see anything due to privacy reasons. On XX/XX/22 I emailed XXXX XXXX, President Maine Peoples United for assistance. He had his senior market manager, XXXX XXXX, call me on XX/XX/22. She told me that because my brother and I were both named as primary beneficiaries neither of us can receive a share until the other signs off. 
I have contacted two local banks and set up a hypothetical situation similar to mine. Both confirmed that they would pay out my share of the funds without requiring cooperation from my brother. I have reviewed a copy of Peoples United Banks Consumer Deposit Account Agreement, specifically page # 5 regarding XXXX XXXX Accounts, and see nothing requiring simultaneous distributions. I also contacted the Maine Bureau Of XXXX XXXX and was told there were no federal or state laws nor any other reasons they were aware of that prevented Peoples United from paying me the funds ; unfortunately however, Peoples United Bank did not fall under their regulations and I should contact the Comptroller of the Currency for assistance. 
To sum up, I was told by the bank that XXXX the funds are now legally mine, yet the bank refuses to convey them to me unless my brother cooperates. The Bank has not provided me with any documentation to show how they have any authority to withhold my funds. I dont understand how they can let a third party, my brother, have influence over when and how they will pay me funds that I understand to be rightfully mine. Please have the Bank provide me with documentation clearly showing what they are basing their position on or, preferably, instruct them to pay out XXXX of the funds to me as soon as possible.