FYI, the word you want here is "who".

https://ielts.com.au/articles/grammar-101-who-vs-whom/

Oh dear, I hate to jump in but “whom” is the correct usage here. Grandparent is echoing great-great-grandparent, and since one pays her, one pays whom

> if you can replace it with “him” or “her,” use whom

Source: parent