ancestry vs family line

ancestry and family line both are nouns.

Word	Noun	Adjective	Verb	Adverb
ancestry	Yes	No	No	No
family line	Yes	No	No	No

As nouns, family line is a hyponym of ancestry; that is, family line is a word with a more specific, narrower meaning than ancestry:

Other hyponyms of ancestry include family, folk, kinfolk, kinsfolk, phratry, sept, side, breed line.

ancestry (noun)	family line (noun)
inherited properties shared with others of your bloodline	people descended from a common ancestor
the hereditary derivation of an individual