Charles Ellicott Commentary 1 Chronicles 24:4

"And there were more chief men found of the sons of Eleazar than of the sons of Ithamar; and [thus] were they divided: of the sons of Eleazar there were sixteen, heads of fathers` houses; and of the sons of Ithamar, according to their fathers` houses, eight." — 1 Chronicles 24:4 (ASV)

And there were more chief men found. —Literally, And the sons of Eleazar were found more numerous regarding the heads of the men than the sons of Ithamar. The basis of division was not the individual members of the different families, but the heads of them. There were more head men, or heads of households, deriving from Eleazar than from Ithamar.

Chief men. —Heb., heads of the men, that is, heads of single families or households; just as “heads of the fathers” denotes heads of groups of fathers or clans. (Joshua 7:16–18.) Of course, as the heads of households were more numerous, the total number of priests claiming descent from Eleazar must likewise have been more numerous than their kinsmen the Ithamarites.

And thus were they divided ... fathers. —Rather, And they divided them: to the sons of Eleazar, heads of father-houses, sixteen, and to the sons of Ithamar, to their father-houses, eight (heads). They (that is, David and the two high priests) divided them (1 Chronicles 24:3).