Poa Named Herself As Beneficiary On All His Accounts. He Died, What Do We Do?

All the information I have is as follows:

My father had a will and his sister was his POA for his end of life and finances. He died recently and when my brother asked when the will would be read the POA called him up to say she has “notes” on what he wanted and will be doing that (giving money to her nieces and nephews, which he had no contact with).

My brother called up the places he knew my grandfather had accounts with and they all stated that the POA made herself the beneficiary on the account so he would have to discuss the matter with them.

My brother spoke to a lawyer who said that he would have to hunt down the will and they could go from there.

Is there anything that can be done? A quick google search tells me that a beneficiary supersedes his will. My dad’s sister is offering a small amount to his kids, but that’s a fraction of the money he had.

Is there anything we can do? When he was alive and the previous copies of his will that we saw designated 50/50 assets to his kids (he has two). Death was in MA

some details are edited for privacy