My mother who has dementia, and my Step-dad who has dementia are both 92. I live across the street from them. Here is my issue. My mother and I have had a horrible relationship ever since I was abour 12. I am an only child. My mother AND Step-father will say the meanest, nastiest things to me. They are very very hurtful words, and it does cut me to the bone. I've been told to consider the situation and realize that they are old and are just this way "to me." I cannot accept this behavior. It is abuse I think! They are not this way to other people. In fact they are sickening sweet to other people and just the opposite to me. My mother has a DNR, however I do not have a copy of it and there isn't one posted in her home. My mother is in rehab right now and so talking to her about this is like pulling teeth. So I told my Step-Dad that I needed a copy of this. He told me that 'I was trying to snuff my mother out'. What a horrible thing to say. If anyone else talked to me the way they do and abused me verbally like they do I wouldn't have anything to do with them!!!!
They have dementia and nothing you can do is going to change them. Even without the dementia in the picture you have not gotten along since childhood. This is how they are. Why aren't you long gone?
If Mother doesn't have a DNR, let her husband make decisions for her. Yes, I know he has dementia. Presumably she knows it too. But in any case this is not your responsibility.
Let go. Back away.
My mother (who has dementia and end stage renal failure) is mostly sweet to other people (lately she's been kind of nasty to some of the home support workers but I think I stomped that out the other day). She can be sweet to me, but she can also be nasty and defiant. The "leverage" I have to keep this bad behaviour down to a dull roar is that 1) my brother and I have shared POA and he supports my decisions, and 2) mom can't remain in her own home without me being her primary caregiver. The very last thing on earth she wants is to be in a care facility. I rarely play the "I'll quit doing this and then you'll have to go live in a care home" card. But I have, several times, and I will again if I need to. I don't feel even a tiny bit bad about it.
You don't say whether you are acting in a caregiver capacity or whether you have POA. I don't know what you can do without POA. If I didn't have this "leverage," I wouldn't be able to continue as her caregiver. I've heard lots and lots of stories about how older people feel more "safe" to lash out at their own family members, as if that's supposed to make it more acceptable somehow. But I will not tolerate mom's verbal abusiveness, and the fear she has of being put in a care home is the only thing that shuts it down anymore.
So....if using that kind of "leverage" is not an option to you, I agree with the others that you should probably walk away. Dementia only gets worse.
Have you considered moving?
My mother made sure to tell me some years back that she could never live in my house. I'm glad she said that, because there will be NO chance that that will ever happen (and I have a ranch house, so I could see some people -- in hospital? -- thinking that could be a solution).
I won't move in to take care of her, not even for a short time say as in a post-hospitalization stay, because I had a short taste of that a few years back and it won't happen again. It will be time for the golden boy brothers to take some time off from their jobs and come down and attend to their mother (that is, if she won't hire care).