How to get my mentally ill elderly father help or remove him from my life?

In the US it is legal to have untreated mental illness.

The only person you can change or make to get help is you.

Move out and take care of yourself.

My family has those with untreated schizophrenia and untreated bipolar. I think the diseases are harder on you and I. Best of luck.

If he physically hits you, call the police to have him removed from the house. Tell them he needs to be Baker acted for Mental illness and refuse to let him back in the house. Baker Act means at least a 72 hr hold. If the house is his, then while he is gone make arrangements to get out, if your house do not allow him back. Tell the authorities that you are afraid for your life and he cannot return. Let the State become guardians. Then he is not your problem anymore.

How old is dad? Elderly doesn't mean the same thing to some as it does others.

How old are you that you are stuck? Because at 18 you are free to move out and live your life on your terms and expense.

Dad isn’t changing, unless it’s to worsen. No one deserves abuse, ever. Please leave and don’t look back. I’m sorry it can’t be different or better, it’s time to look after yourself and build a life with people who bring good things to you

its very hard to force someone into mental health help, unless they are a danger to self or others.
if its not in that scenario, then best you can do is convince him, and tell him the alternatives if he does not do it.

Why are you "stuck in his house" exactly?

If you are over 18, you're old enough to have your own life and your own home. You owe an abuser nothing, even if he is your father. He's not going to seek help nor can you help him to do that. He's an addict and they never change.

Step up and take responsibility for yourself. He's his own problem, not yours.

Why are you messing with this guy?
Can you tell me that?
Do you LIVE with him?
Does he LIVE with you?
And if either of those are true, whose fault is that, exactly?

If you do not want to have anything to do with a mentally ill abusive person I suggest you stay out of their general territory. It may be a good idea to move away across the country so that you will not be tempted to manage the unmanageable.

He will not change.
The only question left, then, is--will YOU?

Since you live with your abusive father, it is YOU who must make the changes and get the h*ll out of there.
Why do you choose to live with someone so abusive? Surely it would be better to be homeless than to put up with his sh*t right?
You do deserve better, but for some reason you have chosen to put up with him and his abuse.
Is it because your father pays all the bills and you're choosing not to work? Or is it because he's gotten you so beaten down that you don't know any better?
Whatever the reason like I already said, you need to get out sooner than later.
A homeless shelter would be better than where you're living now right?
And if you are the one enabling your fathers drinking and pot smoking by going to get both, just stop. You are only making matters worse.
And like already mentioned, call APS in the morning and report the situation, and let them take over his care.
You need to step as far away as possible from him and the situation.

If Dad was always abusive it’s too late for your Dad to change . This is who he is . Whether the abuse is new or not , you should not live with him .

Move out , maybe other family or friend can let you stay temporarily . If he is not able to take care of himself call APS. Does he go out on his own ? If not , who brings him booze and pot? How old is Dad ? Do you have a job ?

You say he is elderly but not how old you are. Assuming you are over age 18 and capable, there is zero reason you need to stay in his house. Do you have a job and a bank account separate from his?

do you have other relatives or friends who can help you move out?

You can call adult protective services in your area and say he is not safe living on his own if you believe that is true.