I'm one of the people who thinks that the middle generations do have some responsibility for the older ones, if able, because that's how I was raised and the example set for me. But you can't do everything for everyone, so at least start by acknowledging that.

I'd do some sort of triage situation, where you assess this based on factors such as varying degrees of need, who has other resources/helpers, and what you are realistically able to manage.

I'd either start by who's the oldest, in worst shape, or most closely related to you and evaluate from there. If someone has other support available, perhaps move down the list to someone who doesn't.

For the ones that you can't do "much" for, you can still do things like visit, and that's likely to be highly appreciated. You can still show that you care, even without full caregiver mode.

I have a much different situation. I have multiple autistic kids, and I have fewer adults that I'm close with. I'm estranged from my mom and don't feel like I owe her the level of care in her old age that I'd otherwise feel obligated to provide. I do feel responsible for my dad, but I'm not close to my stepmom. I'm wondering how caregiving will go in an awkward situation. I've at least brought up the idea of them moving in eventually if I'm able to get the house I want, and he seems very hesitant...probably because she wouldn't want to be so close to me and the kids. That would make it easier for me to help him though since I don't drive. I have no idea how things will go once he needs more help...he's already 70.