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

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