noun, の adjective
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. Just remember there is a rendaku that changes そ to ぞ！
Our family has a special diaper that has been passed down from father to son for six generations.