grand- 接頭辞語族
1世代上: grandfather, grandmother, grandparents
1世代下: grandson, granddaughter, grandchildren
2世代上: great-grandfather, great-grandmother, great-grandparents
2世代下: great-grandson, great-granddaughter。
口語呼び方
grandpa / granddad (祖父), grandma / granny / nan (祖母)。paternal vs maternal
paternal = 父方 (paternal grandparents = 父方祖父母), maternal = 母方 (maternal grandparents = 母方祖父母)。