As terrifying as it is for one day I might possibly experience this myself, it could just be as easy as bliss and blur for me
That's not how dementia works. Dementia is not just memory problems, it causes behavioral problems and widespread cognitive problems. Your brain is literally degenerating (rotting) inside you. It is truly a fate worse than death. It is well known that people with dementia who were excellent people become combative and mean due to their disease. Sometimes it is considered a certain phase/stage "the mean stage".
Lots of stories of people's experiences with dementia on the reddit sub r/caregiversupport, which is a good sub. That can give you an idea of the behaviors seen in dementias. One thing people don't understand about the behaviors is that it's the opposite of a developing child, they can only decline, so any supposed rock bottom you hit is not the actual bottom yet. They eventually lose the ability to use utensils so need finger foods or to be spoon fed, to wipe your ass (can't remember how) etc.
They will spread their shit on walls, put shitty toilet papers in the sink and swear "they did it this way their whole life", use toothpaste as handwash, physically fight being showered, get shit and piss literally everywhere when they try to use the washroom... it's so much shit. My sister worked as a homecare worker once and in a yr a woman with Alzheimer's went from being relatively normalish and able to play cards to chasing her around with a log of poop she took from her diaper bc she didn't know what it was or what to do with it (put in toilet).
Another behavior extremely common in the demented is they have an urge to "wander". Many missing persons cases of the elderly, especially in their 80s are people with dementia who wandered. Same goes for unidentified elderly remains. They are a physical danger to themselves and can be hard to control.
I do not blame Robin Williams for killing himself bc of having Lewy Body Dementia. Canada may legalize assisted suicide via advanced directives eventually. Usually I think the laws go too far but this is honestly a good idea. We should not force people to live with dementia who wouldn't want to put their loved ones through that or live without essentially a soul.
More than one person on the subreddit has talked about how they cared for their relative for decades and now they are in their 70s and their health is being impacted but their 90 yr old demented parent has perfect bloodwork and shows no signs of slowing down.
If you suspect your dad is in the very early stages of cognitive decline, set up a POA, advance directives, if he wants hospice or curative treatment at the end of life or not etc, will, funeral plans. That doesn't even get into the financial issues of paying for memory care or homecare.
Some people think they can be the only caregiver themselves to save their inheritance but they can take a surprisingly long time to die and you will have literally no life the whole time, be on call 24/7, the lifting can cause permanent back damage if you don't get a Hoyer lift and learn to use it right or they are too belligerent or proud to allow you to use it.
Strongly recommend to put your kids first if you have them when considering caring for your parents. Your kid will only grow more and more independent while your demented loved one will only disintegrate before your eyes. Your kids will benefit from your attention and love while your demented relative will not remember or appreciate your sacrifices.
You only have so much to give... remember that. You cannot pour from an empty cup. Memory care and frequent visits are really the only way to stay sane if you ever find yourself in that situation.
Coupled with her suffering from heart failure it’s not looking good.
May I ask, are you going to get her a cognitive test? You can request it from your GP. It sounds like she might have vascular dementia due to the heart problems. I'm sorry, siblings that refuse to help are despicable and you and your sister are good people doing the right thing.
My personal anecdote is I've found that people with vascular dementia tend to be nicer and more docile and Alzheimer's more violent and mean. I don't know if there's anything to back that up empirically though.