父祖 is read as ふそ (fuso) and means ancestors.
ふそ
fuso
ふそでんらい
hereditary
そぶ
grandfather
おじいさん
そふぼ
grandparents
おおおおじ
great-grandfather
こうそふ
great-great-grandfather
がいそふ
maternal grandfather
ぼうそふ
deceased grandfather
ぎそふ
grandfather-in-law
おおおじ
granduncle
ひじじ
そうそふぼ
great-grandparents