My opinion. Once they're adults, you don't owe your kids/grandkids any material things. If the adult child you raised is failing at being a parent to your grandchild/grandchildren, when they're still kids, you do "owe" the grandchildren as much engagement that circumstances (including the law)...
I remember a classroom discussion in 3rd grade regarding what the world would be like in the year 2000. I did the math and realized I'd be 30. (I remember how old I thought 30 was, lol.)
I just turned 50.
Recently turned 50. I also recently retired. I'm married and have two kids, 9 and 10 years old.
My new job since retirement is staying home and taking care of the kids. (I like my new job a lot better than the one I retired from).
Life is good.
Cheers!