Mental Illness and POA.

A door once opened is sometimes difficult to close. Dad's been abusive. Past behavior is often a good predictor of future behavior. If you open the door, your abuser has the means to find some way to hurt you again, so let your brother handle it.

Abusers are the lowest of the low, and it never makes sense to let them back into our lives. Stay as far away as you can from this situation. Your father hasn't earned your kindness, concern for his care or even your respect.

You can almost NEVER get POA from a parent with mental illness. Nor can you get guardianship or conservatorship unless you can PROVE to the court system that the mentally ill person is so ill that no medications can ever help and that the person is an immediate threat to self or others.

Even if you WERE able to be POA or guardian, how far do you think you would get with someone completely uncooperative.

POA is not gotten. It is GIVEN and it is given by the father to the son. And even with POA, unless the father goes into dementia, the son cannot make decisions.

I recommend reading the following memoir.
Liz Scheier's Never Simple.
Ms S. had a mentally ill mother she attempted to help and keep off the streets for several decades and she had the assistance of the entire city and state of New York Social service system. All to no avail. Nothing could be done.

Unlike dementia, mental illness is not considered to be something in which the courts will take a citizen's rights to his own decisions from him.

This mentally ill father is NOT going to give POA to his son or to you.
And to be honest that needs to be the best news you have ever heard.
Because trying to manage someone mentally ill is like trying to manage a cyclone.

This man was always a victim of his own limitations. Never a good dad. Now he is out of control mentally. Report problems at Adult Protective at APS or to the Police. Stay away from him otherwise. If anyone takes guardianship let the state do it. There are times in life when we do reap what we have sown. Get on with your own life and make it a good one so that the abuse doesn't play forward for generations.

Your father has to be willing to designate someone as his POA, and if an attorney finds him incompetent to do that whether because of his mental illness or dementia then someone will either have to file for guardianship(which costs thousands of dollars)over him or let the state take over, which to me sounds like the best plan at this point.
Call APS and report a vulnerable mentally ill adult living by themselves, and let them take it from there.

Mental illness does not make a person incompetent. You brother should be able to take Dad to a Lawyer and have your POA revoked and Dad then assign your brother.