One's Ancestors
Noun and の adjective
せんぞ
うちの家族には、六世代に渡って先祖代々受け継がれてきた特別なおむつがあります。
Our family has a special diaper that has been passed down from father to son for six generations.
Your previous ancestors are your ancestors. All ancestors are previous to you, after all, unless you want to talk time travel, then who knows.
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.