How do you cope with seeing your parents get old and declining?

Basically, they are in charge of themselves and you are in charge of you. Future proofing is in their own hands. Do you have siblings? There are a couple of threads on this board from a few months ago that are worth a read - just scroll down and dip in and out. I think they are along the lines of what I wish my parents had done earlier ….
The thing is you want your parents to see and do the future proofing tasks for themselves of their own volition and not have you suggest them.
Protect yourself and learn about boundaries.

OP, I should also have added I was in your shoes 20 yrs ago and their ‘Give No Fucjs’ phase was probably 25 yrs. My eldest DC is 25 so you can see how it impacts your own life if you choose to fully engage and play be their rules.

All you can do is take on board what's happening and let it influence your own planning. Deal with your own health issues, stay as fit as you can.

Maybe think about what would support you during this time - maybe mindfulness?? Did they row when you were a child? It's incredibly uncomfortable hearing your parents bicker but maybe they've always done it to some extent?

Try and take one of them out to give each other a break from time to time.

Having experienced the decline in health and subsequent deaths of my PIL who didn’t look after themselves at all I would say we learned that you need to pick your battles, we tried to impose what we thought was best when they were at a stage in their lives where in reality the damage was already done.

I tried for years to get my parents to plan.
Unfortunately they both woke up one day and realised they were 90 and they seem to age overnight.
Dad died in sept and mum is now in a care home.
I can’t help feeling that if they’d taken advice from me, they’d have moved into some sort of assisted living and not had the problems they did have In their home.

A bungalow would have been ideal.
however it was their decision and although I’m dealing with the fall out now, I know I tried.

It’s very hard seeing your parent decline. X

I don't understand why they are so resistent to doing the things that might actually help them.

I can totally relate to this - though at a different stage (my parents are older, my dad is my mum's carer, and I don't get why he won't do some of the obvious things that would help with the things that he is understandably complaining about - but I've stopped suggesting altogether).

I was directed to the GEMS dementia classification, and realised that my dad is at the diamond stage. Which doesn't mean that he is on a path to dementia (in fact that should be diamond 'state' not 'stage'). But I think that is where this kind of stubbornness which looks irrational (from the outside) comes from. Recognising it was helpful for me - maybe something similar is going on with your parents?

I haven’t had to cope with this yet as my dad was always pretty ill and passed away a while back and my mum is in great health in her eighties.

I think knowing everything was just going downhill kind of spurred me on to have children ten years ago. I could see the future was funerals and I wanted something positive. Luckily I did manage to have my own family abd that’s what I focus on.

I'm handling it by letting it go. They can and are able to make their own choices. The consequences of those choices don't create an obligation on my part though.

It sounds like they are stuck in their ways. It's hard but all you can do is make suggestions. You can't force or even inspire them to change the habits of a lifetime. I think there comes a time when people don't have the physical or mental energy to take these kinds of things onboard. I know that was certainly the case with my parents.