Power of Attorney for Parent

I wasn’t sure where to post this so I’m sorry if it’s completely wrong. This is long but I need help with this crazy situation that I’m in, please. 🙏🏻 I live in Florida just to put that out there for legal reasons.

My father had three cancerous brain tumors when he was 17 that made him mentally “incompetent” if that’s the right way to put it. So he legally has to have a power of attorney to control all of his finances and medical decisions. Originally, his father (my grandfather) was his agent, well he passed away due to colon cancer. So now his mother (my grandmother) has power of attorney over him.. yesterday was his 40th birthday and no one had heard from him from 6pm yesterday to 5pm today. My sister lives an hour away from him and I live 6 hours away. She drove over there and called the police because his car was there but he wasn’t answering his door. He has so so so many health issues now ever since his tumors and we thought something bad happened to him, we were freaking out. He ended up answering the door and apparently he was sleeping, all he wants to do is sleep. He has a half diagnosed heart condition now. He’s waiting for answers from the doctor but the technician he got the heart test with told him one of his main veins is not getting enough blood. So my sister went in his house and it was horrific. My grandmother will not give him money for food, clothes, cleaning supplies, nothing at all. He didn’t even know if he was going to eat tonight. My sister got supplies, cleaned his house for him, and took him to dinner. Well now, we’re fed up. Grandma here is apparently taking his money and not helping him at all with his medications, doctor appointments, food, nothing. My sister and I want to move him over to me and my family, get power of attorney over him and get him settled in an apartment close to us so we can go over everyday to take care of his house and cook him nutritious meals with his own money. I need help when it comes to transferring power of attorney if anyone is familiar with this we need help. My sister is taking photos of everything, I’m documenting it all, looking into lawyers for counsel, homes for him to live in, we need to help our dad. We had no idea it was this bad. His mother doesn’t even come to check up on him and he’s like rotting. He never told us any of this. We feel so guilty and like we need to do something. I don’t know why she’s taking the very little money he gets from the government (not complaining) but it’s not like she’s making a huge profit, we know we’re going to have to give money from our own pockets to keep him with us. It’s not about the money, it’s about taking care of your family. I’m 22 and my sister is 20, any advice would be amazing. Thank you if you’ve read this whole thing. ❤️