My brother did do anything wrong. My dad told me he doesn't like his attitude but when I mentioned that we were going to go to lunch together when we pick out new shoes for him, my father was okay with this. Why do they get like this? Last week he was mean to my sister and told her not to call him anymore after work because they don't talk about anything different. I explained to him that he hurt her feelings and he didn't even care. He just doesn't want her bothering him. What do you do with this because my brother and sister are hurt? Dad is living with me and my hubby.
We tend to think of dementia as loss of memory, and it does include that. But we may not be as aware that when the brain is damaged it can affect any and every part of the body, thinking, and behavior. (Depending on the nature and location of the damage.)
Urge your siblings to become informed about dementia, and to try very hard not to take these very hurtful behaviors personally.
Sometimes I wonder if our parents might have active imaginations and invent scenarios in their heads that never really happened, then get mad about it. Many times I can't figure out how things go wrong. They just do and we often get the verbal brunt of it. It's not right, but I don't know what we can do except to let it roll off of us.
https://www.agingcare.com/Alzheimers-Dementia