My mom (86) and stepdad (80) with Parkinson's paying caregivers to stay in home, but how to get them to downsize/move to AL or nursing home?

Is this a matter of the couple needing 24/7 care now that is too expensive for them to afford in home? I can only imagine that would be the only reason they cannot continue as is. I would be honest with them that their finances will not last if spent in this manner and that they will be left without the ability to afford in home care and without the funds to find a nicer place to be. You can but explain the facts. You can't force them to accept the facts.

Are you PoA for either of them? If not, is anyone? Do you have insight into their financial condition? I ask because without any legal authority to intercede, and if you can't convince them of a better arrangement, you may need to stand on the side and watch the train wreck, then call APS who will move for guardianship (unless you pursue it for your mom).

You want them to move to AL but can they afford it for 2 people?

I agree with againx100 that you should reduce the amount of orbiting you do to help keep them in their home. You must put up a boundary and tell them you're just not able to do this or that.

I don't blame anyone for not relishing the thought of leaving their beloved home. Moving into a facility is symbolic that one is exiting this world. Also, they may have outdated notions of horrible NHs, so maybe if you can find one they can afford and take her for a visit to see for herself? If she won't go you still can and take video to show her. Maybe the admin would introduce you to some content residents that you can interview. Make the case that her husband's Parkinsons will continue to advance and then what? YOU cannot provide care for 2 people, even if you were willing (and you're not), you literally won't be able.

You must also consider that your mother's grumpiness may be the beginnings of dementia. Has she ever had a cognitive/memory test? If not it may be time so that you know what you're dealing with. She may be depressed and need some meds to improve the quality of her daily emotional life. Lots to ponder. Do a little every day to work on things. If you try to do too much with your mom she can easily feel overwhelmed. Finesse may be the best strategy right now so that there's buy-in and cooperation from at least one of them. Give us an update with how things go. I wish you success in helping them to make wise decisions!

I think it makes perfect sense for them to sell and move into assisted living. They could be together there until one of them declines such that AL no longer can meet their needs. But that's a problem for another day.

If you are doing things to support them staying in their current living situation, set some boundaries and cut back, to help show them that AL is the answer. If they want/need more help, they can hire help with their own money. You can help facilitate that too. It gets to a point where having enough staff to do everything necessary is difficult at best.