Thoughts about having parents

I got into a discussion today with MS and his father-in-law. DrB is 77 and suffers from both Parkinson's and Alsheimer's. DrB still lives with MS and PS. And I imagine the caretaking of DrB is wearing thin on MS and PS.
Now, neither of my parents went through these two challenging conditions. But I think it may be time for MS and PS to allow a nursing home facility to look after him. MS made the comment to me that he's grown weary of constantly looking after DrB while at home.
I guess the question is how much of his/her quality of life does the child have to sacrifice to take care of a parent? I know this question has always been around as long as there has been parents and children. My quality of life never really suffered as I went through the loss of my parents, but I know there are people out there who put there lives on hold.
I wish MS and PS the best as they address future issues with DrB.