If you are named as a 1/3 beneficiary of an account, does a will override the beneficiary of said account?

Does the POA have to prove where "funds" went from savings accounts? I am aware of quite a difference in what should be in one of the accounts and the noticeable depletion in the funds in this account....appears as if funds are being used for reasons not for the benefit of my mom....so wrong! Also, can you trace where proceeds from the sale of an expensive vehicle goes? Assets are being sold and stolen left and right and there appears to be NO accountability. And my mom is still alive (not competent, however). I cannot afford an attorney and DCF or any other hotline has not been able to help.

A POA can change it if that is the wish of the person, but a POA can NEVER change anything to benefit themselves. That would be illegal in all states.

The title of an account and the beneficiary stated on that account is how the asset is distributed at death. The Will is only for assets that do not pass by title or beneficiary. If the POA's document states that such changes can be made, then it can be done ---prior to death.