stemma vs family line

stemma and family line both are nouns.

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

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

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

stemma (noun)	family line (noun)
an eye having a single lens	people descended from a common ancestor
the hereditary derivation of an individual
a tree diagram showing a reconstruction of the transmission of manuscripts of a literary work