Losing my mind and will to live. I honestly don’t know what to do anymore.

I take care of my grandfather. He’s always been a negative narcissistic person. But it’s getting worse. He makes himself feel better by putting us down or criticizing us every chance he gets. It’s nothing new. He has done it as long as I can remember. If we show any signs of happiness. He is quick to throw a tantrum to bring us down. He’s had several mini strokes and is literally out of his mind. I believe he is incompetent. A danger to himself and others. He has firearms and I want to lock them up away from him. I do not trust him anymore. But if I do, he will go ape s&$t. He doesn't bathe. Has dogs that stay inside that he doesn’t wash. They are covered with fleas. And as much as I try, he just lets them back out to get covered again. I’ve had to hide pesticides from him so he won’t spray them indoors. He uses posisons meant for a garden. When he can’t find them he throws a tantrum. He has no concern for others. We live in a rural area. I’m at my wits end with him. I’m severely depressed. Have major anxiety. My health is in a decline. I do not know what to do. Doctors are pointless. He just argues with them and insults their opinion. Does not take his medication as directed. Me and my mother are the only ones who take care of him. My mom can’t do much. She cant drive. So I’m stuck with pretty much all the responsibility. My uncle has no contact with him really. like I said he’s always put us down and criticized us. And I’d imagine he wants no part of it anymore. And I’m almost at the point where I don’t either. And just let him stay in his own filth and die. I have given up the last 10+ years of my life to take care of my grandparents. I’m at the point where if I don’t get away or get help I won’t make it til next year alive. Is there anyone else in this situation? How do you cope with it? How can I not let his rude narcissistic put downs affect me? I do not want to be medicated. But I feel hopeless, lonely and full of anger. I honestly don’t know what to do anymore.