Grandmother Trying To Steal Our House

Location: Florida Long story but I want to be precise. My grandmother bought a house about 23 years ago. She took a handshake loan from my uncle to place a down payment which she never repaid. My father has paid her mortgage off and on since about 20 years ago, and has been the sole payer for 11 years. Last year she signed a new deed placing his name next to hers so they are 50-50 owners. He is in the hospital with sudden onset dementia and I am working on a power of attourney so I can take care of his legal and civil issues. I have his full permission to live in the home indefinitely. She is 88 years old and it’s harder for her to take care of the home with me across the state 5 days a week caring for my dad in the hospital. She’s threatening to sell. What are my options? My father would obviously never agree to a sale but he’s also not competent. We have no will so what if he dies before her? Will a power of attourney make me the de facto half owner? I don’t want to kick her out. It’s the family home and she deserves a place to live. I just don’t want to lose the one thing my dad has to show for his life. And I don’t want to lose my home, obviously. Edit: a few more details. I say “steal” because she seems under the impression she can simply revoke the quitclaim deed and take all the money from the sale. My father and I have been repaying the loan from my uncle as well so she has very little financial investment in the house.