Practically, it's unlikely I'd be able to, given the ages of my DCs, that they will both still be at school if my Mum needs care at the age her mum needed care (both my brother and I had left Uni and left home by then, and both my parents were working only part time on a wind down towards retirement).
Having seen how hard it was mentally, not just physically, for my parents to look after my grandmother who was healthy in herself, but had dementia, and then the high quality of care she got in the home she went in when it got too much for my parents, I'm not sure I would take that step lightly.
It was like having a pre-schooler, that had to be constantly watched, monitored, could never be left and yet you couldn't hire a babysitter for a night out or send them to a nursery. She would talk constantly like a toddler, was too big to just pick up for she decided to throw a tantrum (again, like a small child), would go round switching on fires and cookers or unplugging the freezer...
It was mentally draining for them, and I'm not sure I could cope (they didnt very well and should have given in and used a home earlier), and there's no way I'd put my DCs through living with someone with dementia.
When people blithly say they'd look after elderly relatives, the assumption seems to be doing their gardening, cleaning and the big shop for them, or helping them in and out of the bath, taking to appointments etc.
Not hiding the car keys so they won't take the car out and smash it again (driving licence long gone, but so was the memory that the driving licence was gone...). Or having to rehome the cat as Nana's decided it's a pest and has taken to throwing things at it and won't be told it's their cat. Or having to install fire doors and locks on the cooker. Or getting your gas fire disconnected to make the whole house safer as she won't be told not to mess with it. Or walking into the kitchen to find every single cupboard has been emptied, but Nana hasn't a clue why she did it.
It's constant, and can be a decade or more of care. And unlike a small child, it just gets harder, not easier as time passes.
So no, I won't move my or DH's parents in. I will get them good care, and will look after their finances and visit, but not take them in.