Really really don't want to care for parent

Don't do it. Your children are your responsibility, your parents are not. As you say in your post you don't have the time and don't want to. This is reason enough.

Tough one. Very. Was this situation a surprise ie did they see it coming and ignore it?

I think most people don't want to and don't care for an elderly parent, especially if we're including men. Lots of parents don't need care, others will organise it for themselves, some die young. It's a small minority who are doing the hands-on stuff.

I'm not doing the hands-on stuff. I still end up doing a whole ton of stuff though - worrying, organising, accompanying, shopping etc. It can be hours and hours or even days every week and it's very unpredictable. And I really resent it and feel I didn't sign up for it. I keep thinking, what do those without children do. They manage or they die younger or the state steps in. I have many talents but, like you, I don't feel caring is one of them.

Someone on this board gave a brilliant quote from Phillipa Perry - if you have to choose between living with guilt or living with resentment, go for guilt every time. Honestly if they have funds to pay for care, you can be clear about what you're prepared to do (and nothing is fine) and perhaps offer to help them hire carers, but no more.

Say "no" to whoever is asking you to do it if it's not your parent. If it is your parent be crystal clear it's never happening.

My mum tried to get me to be a carer for my Dad a couple of times but I stuck to my guns and said no, for similar reasons to you've given (quite how I was going to manage this with two small children was beyond me).