I grew up as the child in this situation.
It was fucking horrific and the issues stemming from it have permanently scarred me. We no longer speak to an entire branch of my family due to the perceived injustice around elderly care between siblings (my parent and their 3 siblings), they were cut off before I knew them, I was too young. My mum was the instigator of this stupid idea due to some unrealistic rose tinted assumptions, and it ruined her relationship with them too - what was an involved grandparent became suffocating and financially my parents couldn't ever afford to move further out again, because that's where the care needs started. There was a lot of resentment, missed opportunities and simmering frustrations towards the end when I moved away as a teen myself, eager to flee the nest too soon.
The very idea of my parents or in laws moving next door is literally the stuff of my nightmares.