@whitetaildeer, welcome to the thread, and thank you for sharing your story. It sounds like you have been through quite a bit. I'm sorry that life has played out this way for you, but am glad you're starting to think about living as an option. And with a trust fund coming due in a few years, I think you actual have more options than you think. I think you have an exit from your current life - an escape to a life that will allow you to put your past behind you and look to the future.
I see your tag line places you in the Midwestern US. Are you near a good-sized city? If so, find an attorney and set up a meeting with them. Most attorneys will provide free consultations, but do your research - find an honest and kind one. Believe it or not, they do exist. Also make sure who every you choose has no ties to your family. Explain the whole situation to them, including the PTSD, your father's interest in a conservator-ship, the trust fund, your hopes and dreams.
In my mind, I would hope that they would help you be declared independent, open a new bank account just in your name, potentially get a loan using the trust fund as collateral, and point you in the direction of where you can begin to get help for your PTSD, find some food and shelter, and education so you can find a job you'd like. (What sort of things are you interested in?)
You deserve to be loved, to live free of fear, and have the freedom to things you're interested in. Most of all, you deserve some peace from all of your struggles over the past years.
You're welcome to contact me here or on Discord if you ever want to talk - no strings attached. I don't have all the answers, but have been around enough decades to see a variety of viewpoints.
Regardless of your next steps, I truly hope that you can find peace, and maybe even some happiness.