Patience and frequent breaks. There’s no right answer just keep in mind that they are most likely very frightened and fragile, emotionally if not physically.

They are family most likely. Respect your elders

That's a tough one. I wouldn't say put up with them, but rather cope with them.

My dad had Alzheimer's, at first he would forget things like what he did two days ago.
Then the terrible disease progressed rapidly and continued to take more of his mind. He finally got to the point that it was like talking to a child with him.
He was easily confused and could forget where he was even though we never left the home where he lived.

His mother had dementia (I don't think it was called Alzheimer's yet) then he had it. I already have a minor brain injury, and I have seizures from it so I'm a good candidate for having it as I age.

Try not to think of it as putting up with them, they can't help it and they certainly don't want to be that way.