‘Zillah bore Tubal-Cain, he was the forger of all instruments of bronze and iron. The sister of Tubal-Cain was Naamah.'
Tubal-Cain was the one who shaped metals. Mitchell (NBD) suggests that perhaps ‘he discovered the possibilities of cold forging native copper and meteoric iron, a practise attested archaeologically from prehistoric times'. We do not know what Naamah (meaning ‘pleasant') did but she must have been very outstanding or notoriously beautiful to be named at all.
Notice that three sons are named, as with Noah (Genesis 5:32) and Terah (Genesis 11:27), in their case instead of ‘other sons and daughters'. Three was an indication of fullness and completeness (in ancient Sumerian religious literature the numbers three and seven were used almost exclusively because of their significance as meaning ‘complete'). They may have had others but they are not named.
So Lamech's family built up an enviable reputation for invention from which the line of Seth would benefit. The Flood would wipe out their family but their inventions would be preserved and are remembered with gratitude. Yet probably the compiler considers that it brings out the contrast between these ‘worldly' men and the line of Seth, conveying the lesson that achievement means nothing without obedience.