Honestly, you are potentially on a cliff top waiting to fall off here. I hope I'm wrong but based on my experience over the last couple of years and particularly the last nine months, I won't sugar coat it.
If they are living in a house with no downstairs facilities or stair lift that needs to be a priority. As PPs have said, could you move them closer to you? I would also suggest they really need to be in some kind of assisted accommodation.
Make sure you have copies of anything medical and financial...NHS numbers, regular prescription meds, banking, bills, council tax, house deeds etc.
Setting up online banking that you can access if need be is a good idea. Also online shopping, repeat prescriptions (Do they currently get and meds they need delivered? If not that too?)
Don't rely on them getting good with mobile phones. My mum was senior PA/administrator and is pretty tech savvy but her ability to manage mobiles and even the internet is diminishing rapidly. This is a woman who organised her own will and POA and those of a handful of relatives and until a few years ago would gamely fix cars and ovens with just a YouTube video for assistance. The impact of age and stress hits hard and fast at times.
Bear in mind that it is not just practical support they will need but also emotional support, particularly when one of them is left on their own, which is why I would suggest assisted accommodation of some kind. Unless of course you are willing and able to be an emotional crutch indefinitely, because there is a good chance it will come to that at some point.
My dad had a serious fall downstairs two years ago and broke his back in 4 places. No spinal cord damage and was able to walk again but has never been the same since.
He took to his bed last March and in April we were advised that he was 'end of life'. The GPS suspected gastrointestinal cancer but he was too frail for tests. Based on their prognosis we were told me may have 1-3 months.
Dad is still with us. He is now completely bedridden & doubly incontinent. He often needs feeding, and his speech is poor which limits his ability to communicate. This is further hindered by the fact my mum is now extremely hard of hearing.
In recent months he has suffered from episodes of confusion/agitation/delirium and is often in pain to the extent of needing oral morphine, although of course we don't know what causes it as he is too frail for any more than the most basic of tests.
So we are assuming now that he has severe frailty. There is now treatment or cure and as long as his vitals (pulse, blood oxygen, heart rate) are ok, there is no medical intervention that can be given.
All we can do is plod on until he passes on peacefully of old age or there is a crisis (these are the words of two GPs who have seen him recently).
We have NHS carers come in twice a day to wash and change him but otherwise we're on our own. Mum has long wanted to move to a bungalow or have a downstairs shower room put on, but dad always blocked it, so now at 81 she's having to go up and down the stairs multiple times a day to see to him. I get called out frequently late at night or in the early hours of the morning because unfortunately it's not possible to time the bowel movements of an elderly man.
Because he has no formal diagnosis Macmillan and Marie Curie won't get involved and the local hospice has rejected at least 2 GP referrals for him in the last six months.
I am an only child and we have no other family support. By August I was suicidal with the stress of dealing with it all, particularly the level of emotional support my mum needs. I was signed off work at the end of October and am now taking an unpaid career break in order to care for them. As awful as it sounds I am 10 days in and praying that the inevitable will happen and I will be able toget my mum sorted out before I return to work in September. I have no idea what I'll do otherwise and feel like my own life is basically on hold now until they both pass.
I'm also a single parent to 16yo DD who is doing her GCSEs.
I'm sorry for such a long post and that it's doom and gloom, but I know from bitter experience how easy it is to think only about the basics or that you have time to make changes further down the line, and my parents are younger than yours.
Please give it some serious though, particularly in terms of what you are able to manage, and get as much as you can put in place as soon as possible.