וְאֶחָיו֙ לְמִשְׁפְּחֹתָ֔יו בְּהִתְיַחֵ֖שׂ לְתֹלְדוֹתָ֑ם הָרֹ֥אשׁ יְעִיאֵ֖ל וּזְכַרְיָֽהוּ׃
און זײַנע ברידער לױט זײַנע משפּחות, זיך יחוסנדיק לױט זײערע געבורטן, זײַנען געװען: דער הױפּט יעִיאֵל, און זכַריָהו;
Rashi
tracing their genealogy to their generations; the heads were Jeiel and Zechariah The meaning is: I traced only part of the genealogy of Reuben, but the main part of his genealogy is in the chronicles of the kings of Israel. Jeiel and Zechariah were the heads, through whom their genealogy was completed.