My dad (who passed away last year) had dementia related to Parkinson's Disease. Because I work, I hired an agency to provide live-in caregivers for the past 5 or 6 years. That worked out quite well. It's just fortunate that he had enough money to pay for that service, because it's not covered by Medicare.
I still had to do his grocery shopping, other errands, take him to doctor appointments, etc. And take care of his bills, taxes and all other finances. It was a lot of work, but not like doing it full-time. My hat is off for those who are full-time caregivers -- it's the hardest job in the world. Most caregivers for people with advanced PD will tell you that the dementia/cognitive changes are much harder to cope with than the physical problems.
Now my father-in-law seems to be developing memory problems. It doesn't seem like Alzheimer's, it's quite puzzling. I already have been helping him with his mail, bills and other paperwork, but I am expecting that he will need a lot more care in the future. He has long-term care insurance, but it won't cover everything.