My Great Grandfather Is Developing Dementia And Someone Is Trying To Take His Pawer Of Attorney Or Guardianship Against His Wishes.

I live in PA. My great aunt who is my great grandfather's oldest daughter (not biological) has been trying to take my great grandfather's power of attorney or maybe get guardianship of him to separate him from his current family for some reason I don't really know all the details of. She has convinced herself that we are tormenting this man, stealing his money, making him live in a roach filled mess. None of this is true. She already called a social worker on us who was confused by the claims and impressed with how well taken care of my grandfather is. He also gets help from senior services that come in often and know everything is fine. I have been staying with him for the past few months to make sure he isn't alone and can get medical help if needed. I have already saved him from 2 life threatening heart attacks in this time. Over a year ago my great grandmother died and my grandfather's oldest and youngest daughter's took care of his bills and groceries since he can't handle those on his own. At this time my grandfather made it known that he wanted his youngest daughter to be his power of attorney and handle all of his decisions for him when he died, but nothing came of this right away because everyone was busy for a few months. In the mean time his oldest daughter mailed his bills for him while his youngest daughter took care of transportation, and groceries. After a few months his oldest daughter wasn't paying all of his bills and he got a power shut off notice. He wanted his checkbook back to give to his youngest daughter to take care of the bills. The electric bill was supposed to be set to auto pay after that but my grandfather accidentally canceled the bank card it was on and he wasn't paying the electric bill for a bit. We never got a notice for this electric shut off, but his oldest daughter came to visit the day before. She would have seen the notice, but purposefully didn't say anything so when the power did go out she can throw a fit over it and convince my grandfather to stop letting his youngest daughter pay his bills. After this she used his dementia to build up lies and trick him into going to a power of attorney meeting and made him make a new bank account. She works as a postman and used her position to have his new bank card and check book mailed to her and then rerouted his and his deceased wife's mail to her house so no one from his current family can get ahold of it. It's been half a month and she has yet to buy him any groceries, so one of my other relatives has been having to pay out of pocket for him, and we have no idea if she has any legal power over my grandfather's decision. I don't know how to check but if she doesn't she has committed mail fraud and openly admitted to doing so. If she does have power I have no idea how we can begin to contest it and prove she hasn't been acting in his interests because of my grandfather's dementia. What can we do?