Notes on the Bible, by Albert Barnes, [1834], at sacred-texts.com
Whose number was in the days of David ... - The writer would seem by this passage to have had access to the statistics of the tribes collected by David, when he sinfully "numbered the people" (marginal reference). The numbers given in Ch1 7:4-5 probably came from the same source.
Three - In Genesis, ten "sons" of Benjamin are mentioned; in Numbers, five (marginal references). Neither list, however, contains Jediael who was perhaps a later chieftain. If so, "son" as applied to him means only "descendant."
It is conjectured that Becher has disappeared from the lists in 1 Chr. 8 and in Numbers, because he, or his heir, married an Ephraimite heiress, and that his house thus passed over in a certain sense into the tribe of Ephraim, in which the "Bachrites" are placed in Numbers Num 26:35. He retains, however, his place here, because, by right of blood, he really belonged to Benjamin.
The lists here are remarkably different from those in marginal references Probably the persons here mentioned were not literally "sons," but were among the later descendants of the founders, being the chief men of the family at the time of David's census.
These were the sons of Gilead - i. e. these descendants of Machir were reckoned to the family of Gilead. The name "Gilead" prevailed above all others in the line of Manasseh, the term "Gileadite" almost taking the place of "Manassite."
Abiezer - His descendants formed one of the most important branches of the Manassites. They furnished to Israel the greatest of the Judges, Gideon Jdg 6:11, Jdg 6:24, Jdg 6:34, and were regarded as the leading family among the so-called "sons of Gilead.
The sons of Ephraim - The genealogy is difficult. It is perhaps best to consider Ezer and Elead Ch1 7:21 as not sons of Zabad and brothers of the second Shuthelah, but natural sons of Ephraim. The passage would then run thusly:
"And the sons of Ephraim, Shuthelah (and Bered was his son, and Tahath his son and Eladah his son, and Tahath his son, and Zabad his son, and Shuthelah his son) and Ezer and Elead, whom the men of Gath slew" (i. e. the settled inhabitants, as contrasted with the nomadic Hebrews, Amalekites, etc.).
Sherah could scarcely herself have built the Palestinian cities here mentioned, which must belong to a time not earlier than Joshua. By "she built" we must understand "her descendants built."
Shamer; Ahi, and Rohgah - Translate as: "The sons of Shamer Ch1 7:32, his brother, Rohgah, etc."