I don't doubt your resolve at all! I think we all just want to make sure that you take care of yourself too. It is way too easy to do forget to do that. And if you do, then regret and resentment towards your family can sneak up. I've been there, I had to help care for my adopted father after his stroke as a teen. When most everyone was hanging out with friends, I was at home babysitting him. For the most part, I didn't mind. But there was days, where anger and resentment would boil up, and I'd have a hard time keeping my cool. I would have to remind myself over and over again that it's wasn't his fault.As far as contacting a lawyer, I really can't help but feel I'd be betraying my dad if I did that And really, I DO want to be near my sister as I said before. I know people here think that at 25, I should working on my career and thinking about myself. Sorry but my family trumps that for me. I love her too much.
And IMO if your dad is physically and financially abandoning your sister, then he's the one who betrayed her. And going behind his back might not be necessary. Have a serious cool headed talk about her care with him. Maybe he'll sign everything over to you. But definitely if you are going to be her sole caregiver, then you need guardianship. I'm not 100% sure of the laws, but you might not be able to consent to anything involving her medical or educational needs without it.