Albert Barnes Commentary 1 Chronicles 1:36

"The sons of Eliphaz: Teman, and Omar, Zephi, and Gatam, Kenaz, and Timna, and Amalek." — 1 Chronicles 1:36 (ASV)

Timna — In Genesis 36:11, Eliphaz has no son named Timna. However, he does have a concubine by that name, who is the mother of Amalek and is thought to be Lotan’s sister (1 Chronicles 1:39).

The best explanation is that the writer is thinking of the tribes descended from Eliphaz rather than his actual children. Since there was a place called Timna inhabited by his “dukes” (1 Chronicles 1:51), he includes the people group who lived there among his “sons.”