My MIL passed away from complications due to Parkinson's. She was in her late 60's. I certainly can't help you much with the medical details. MIL was fairly lucid until her very last days. I don't really have anything to help out with that.
She had been diagnosed 10 years prior to her death. The last 8 years she was not able to go out, but that was in large part due to severe arthritis in her legs and hips as well. SIL cared for her up to the end and it was a lot of work, but very lovingly and selflessly provided. MIL was never "combative" about her meds, which were of utmost importance that she take. But she WOULD get stubborn about some things. For example, she'd be sitting there and say, "Let me make us a cup of tea." Now, she could barely WALK, but she would try to always be the perfect hostess. It would take DH and SIL both to convince her that someone else could make the tea.

I will add that they are in Turkey and over there, not caring for elderly loved ones is simply UNHEARD of. I couldn't guarantee this, but if I were to guess, the only "homes" for the elderly are probably for those that have no family and are state-supported.
SIL did all of the cooking, shopping, cleaning, bathing, etc. but still had time to care for her own family. She was tired a lot, though. Never even left the city for years because she couldn't be away from MIL. The last several months were hardest because MIL was eventually bed-ridden with a catheter and IV. Being thousands of miles away, the only thing we could do was to help out by paying for a woman to move in with MIL to help SIL in the daily care of her. (That and visiting as often as we could those last few years... two or three times a year.) In those last few months, one person (SIL) could NOT do it all. Help was essential. MIL knew her days were coming to an end and asked to not be taken to a hospital. She died at home with her loved-ones around her. We even were able to take a last-minute trip to Istanbul to see her a couple of weeks before she passed away. Then of course, we were back there again for the funeral.
I think it's wonderful that you are considering doing this for your FIL. Since you were the caregiver for your mother, you know about the ups and downs of caring for a parent (my own mother lives with us, too

), but I think every person and medical situation is different. I would definitely pin a doctor in a corner and insist on knowing the whole story before you commit to this. I know that with this disease, sometimes one single caregiver may not be possible, even as much as you'd like. Can the state provide a home-nurse to help if things get too complicated? I remember that my paternal grandfather wanted to die at home and I'm pretty sure it was the VA that provided the nurse for him the last few months.
Well, I hope any bit of this helps. I understand (but don't know first-hand) what you're going through. Best of luck and blessings.