I am a fellow only of aging DPs in Scotland, although I am a bit closer at an hour away, which brings its own particular challenges in terms of expectations ( mostly self generated) in terms of frequency of visits, particularly as things have spectacularly deteriorated in the last month.
Do you have power of attorney? If not then a discussion about that and getting the wheels in motion is one of the most useful things you can do. A friend told me to get this set up on their accounts in advance of needing it, and it’s been very useful over the past month to have a debit card for their account so I can set up a cleaner, do online shopping for them and check on the account. Depending on their finances, they may be amenable to paying for your flights to visit. I know this sounds dirty and money grubbing, but in my case it means it’s “just” costing DH and I most of our free time and not impacting our own finances.
The second thing is to decide if either of them might be eligible for attendance allowance. If they have any recorded medical conditions, it’s definitely worth filling in the form with them, next time you are up.
Can you research local cleaners and see if they would accept someone at least weekly. It means that there is someone coming in who - whilst clearly not a medical professional - can report back to you. I wish I had pushed more for DPs to get a cleaner once I got DM full attendance allowance, rather than having to wait until the wheels fell off the bus because she was so blinking stubborn about it.
As they are in Scotland if they are deemed to be unable to look after themselves then they would be eligible for carers up to 4 times a day. This normally relates to a medical issue or hospital stay.
I would also talk to them about it, try and understand what they want. It’s easy to avoid the discussion, and often pointless as my DPs seem to have forgotten anything we previously discussed about the level of support I can provide whilst working full time, the human desire for self preservation is stronger than anything else when it comes down to it.
Also I am learning there is a gap between how I would like the situation to be, and what is acceptable and what my DPs want right now. Ideally for me DF needs additional support whilst DM is bed bound to help with shopping and meal preparation and reminding him to take his meds as he is getting forgetful, but neither of them will accept that. So I go up at a frequency that is sustainable to me, rather than what I think they actually need as they refused the additional cleaners hours or paid for carers.
Sorry one more thing, once you have the practical stuff in place, try to stop worrying about it. When the inevitable happens it will likely be different from how you envisaged it and you will need different coping strategies to manage it.