Both of my grandmothers had dementia. One had Alzheimer’s and the other had a different kind (possibly vascular?) which lasted for decades.
They both went through bad times, but overall, it was nowhere near as bleak as people tend to say. I honestly believe they were happy and contented most of the time.
Both went through phases where they were struggling to manage at home, but reluctant to move into residential care - that wasn’t fun. My grandmother who had Alzheimer’s became touchy, paranoid and sometimes aggressive - she had the delusion that everyone around her was trying to steal from her. For example, she was convinced that her neighbours were trying to steal her washing.
Both of my grandmothers settled well into residential care. I suppose their abilities declined somewhat, as they had less to do, but the pressure was off them and they seemed much calmer and happier. They made friends and enjoyed the activities provided by their homes.
My older grandmother, who had an undiagnosed type of dementia, spent about eight years in residential care. A few years before she died, she went through an unhappy phase lasting several months during which where she refused to get out of bed, and would hit her carers when they tried to get her up. We thought she must be nearing the end, but surprisingly, she got past this phase and regained some kind of normality.
A couple of weeks before my younger grandmother died (aged 82), my mum and I went to visit her. We looked through an old family photo album together and my grandmother really enjoyed this, even though she was a bit confused about who we were. At one point she said, “oh, it’s so nice to have old friends together!” Later she seemed concerned about me, and held my hand. “Will this little fellow be all right” , she asked anxiously. “How will he get home?” Mum reassured her before we left.
The last time I saw my grandmother, she was ill with a UTI and fast asleep. My other grandmother also died peacefully from a UTI. Neither reached the stage where they couldn’t walk or talk, although my older grandmother rarely spoke in full sentences towards the end of her life. At one point, she said “well, well, well” and my Dad replied, “three holes in the ground”, which made her laugh. That was a rare moment where he felt he connected with her.
My only advice, for what it’s worth, is to accept that people with advanced dementia go into a new state that is somewhat childlike. Sometimes they will assume they are in an environment from their younger days. For example, a retired teacher may think they are in a school and in charge of the class. A retired removal worker may think they are on a job and pile the furniture up in the middle of the room.
It’s generally agreed that it isn’t helpful to a dementia patient to argue about this, so try to step into their world with them (as we often do for children enjoying pretend play). “It’s break time/ time for a break” can be a very useful phrase.
Distraction also helps. For example, if the person with dementia is upset that one of their relatives died several years ago, I would acknowledge their feelings, then divert the conversation on to something else entirely by showing them a new object or photo. One of the few blessings of dementia is that people with it often get to bypass grief somewhat.