John Gill Commentary 1 Chronicles 5:7

"And his brethren by their families, when the genealogy of their generations was reckoned: the chief, Jeiel, and Zechariah," — 1 Chronicles 5:7 (ASV)

And his brethren by their families
Either the brethren of Beerah, or the rest of the posterity of Reuben:

(when the genealogy of their generations was reckoned; )
either in the times of Jotham and Jeroboam, (1 Chronicles 5:17) or at the time of their captivity, as in the preceding verse:

[were] the chief, Jehiel, and Zechariah ;
these were the principals or heads of their families.