This is a highly subjective question.
My grandparents had 8 children, all of whom worked FT. Most of my aunts and uncles lived at least 1/2 and hour away from my grandparents, but my family lived 5 minutes away by car. In the summer time my sister and I took turns riding our bikes to my grandparents' assisted living apartment and we helped care for my grandpa (who had Parkinson's) and to help my grandma with her chores.
On the weekends my aunts and uncles took turns visiting, helping, running errands, etc. Whatever needed to be done was done. There was no fighting about it.
If we love our parents, we will take care of them. If we love our grandparents, we will take care of them. If we are not selfish, we will take care of those who took care of us.
I would think that adults can figure it out fairly and whoever has the time and the means to help woudl jump at the chance. Those who are busier will need to give up something in order to help.