Motto

Vergil, Aeneid 7.56 (avis atavisque potens) might make a good family motto, unless one considers that the hero to whom it refers, Turnus, came to a bad end. Translators seem reluctant to render it literally, e.g. Theodore C. Williams (of a line of mighty sires), H. Rushton Fairclough (of long and lofty ancestry), J.W. Mackail (of long and lordly ancestry), Robert Fagles (strong in his noble birth and breeding), Nicholas Horsfall (strong in his line of forbears [sic, read forebears]).

Allen Mandelbaum comes closer (he had mighty grandfathers and great-grandfathers), although he transfers the adjective away from Turnus to his ancestors. Although atavus (whence English atavism, atavistic) can mean any remote ancestor (Oxford Latin Dictionary, sense 2, citing Vergil's phrase), strictly speaking it means great-great-great-grandfather (id., sense 1), and so I would translate the phrase, in my pedantic fashion, as mighty in his grandfathers and great-great-great-grandfathers.

See the list of ancestral kinship terms in Plautus, Persa 57 (tr. Paul Nixon):

My father, grandfather, great-grandfather, great-great-grandfather, great- great-great-grandfather, and his father, too...

pater, avos, proavos, abavos, atavos, tritavos...

On this line from Plautus see Alessandro Buccheri, "The metaphorical structuring of kinship in Latin," in William Michael Short, ed., Embodiment in Latin Semantics (Amsterdam: John Benjamins Publishing Company, 2016), pp. 141-175 (at 155-160).

With Vergil's combination avis atavisque compare Varro, Menippean Satires, fragment 63 Astbury = 69 Cèbe (avi et atavi nostri...).