Listen to your aunt.
There are many different POA forms out there and they can be customized to fit specific circumstances. First, you need to read the POA you have very carefully to determine what specific authorities it provides. It may or may NOT include any authority to make medical decisions on his behalf. If you've needed to step in because your dad was incapable of handling a billing issue, sounds as if this is more than timely. You should plan to get clarification while he is still capable of expressing his wishes.
In general, durable POAs deal with
financial decisions, not
medical or quality of life issues. You need to read yours and/or discuss it with the attorney (hope you engaged one!) who prepared it for you. Making a decision about medical services he is obligated or not obligated to pay is not the same as deciding what therapeutic treatments he should or should not have, does or does not want. That is a very different can of worms that delves into ethical, religious, and personal beliefs.
Just one of a number of articles that may help:
https://www.legalzoom.com/articles/w...er-of-attorney