How can I become power of attorney for my father who has late stage dementia?

Talk with an Elder Law attorney in your state. If your father has lost capacity to make financial or health care decisions, you will need the authority of a Court to manage his affairs, unless he designated an alternate person to step up and serve as his agent.

Probate Court Guardianship supervises a person's medical care. Conservatorship oversees a person's financial matters. If an elder loses the ability to communicate informed decisions, someone else must speak for that person. If you are willing to serve, you can petition to ask the Court to give you authority. But there are costs and time commitments. An Elder Law Attorney in your state can explain your options. If your father is needy, there may be programs in your state that provide legal services and professional guardianship services. But you have to consider the loss of control that goes with assenting to have others act on behalf of your loved one.

Also, who is named a successor POA in the POA itself, after your sister? Does the POA have any language regarding your sister being able to name another POA if she is no longer able or willing to continue?

If there are no successors named or no succession rights in the current POA, 97yroldmom is correct. From a legal perspective, he has to have capacity and competency to execute a new POA and it sounds like he's past that point. Guardianship and conservatorship (if separate in your state) would be an option to consider. I second the suggestion to consult with an elder law attorney for further assistance.

Hi Ralph.
I'm sorry but it doesn't sound like your dad is able to give you a power of attorney in his current condition. He is the only one who can sign as POA for himself.
I would suggest you see an elder attorney and see what you are able to do. Usually guardianship must be filed for and awarded by the courts when the person is no longer competent.
Is it possible that your sister would consider continuing? Perhaps she would visit the attorney with you to discuss dads options and her possible responsibilities to continue as his POA.