Understanding what overrides a beneficary on a bank acct. or a living will

What is the name of your state (only U.S. law)? New York,NY

I have a father who has been diagonise with a new tumor on the brain in a different location from his last tumor. He also has cancer that has spread through his lungs, liver and abdonmal. So the family is feeling that he is becoming incompetent because he has taken his children off of his bank acct. as beneficiaries and added someone who is not a next of kin, but he has a living will that he drew up before he went into the hospital last year. So what I'm asking is that even though he has put someone else as a beneficiary of his bank accts. Does the living will overrides that decision? If not, what do I need to do?What is the name of your state (only U.S. law)? New York, NY

A beneficiary will be the owner of the account on death of the principal.

A living will has nothing to do with the transfer of assets on death.

Please feel free to explain to the children that this never was their money in the first place.