Eliab, called also Elihu, 1 Chronicles 27:18, unless that was another person, and the word brother to be taken largely for a kinsman, as is frequently used.
Verse 14: Nethaneel the fourth, Raddai the fifth…
Verse 15: Ozem the sixth, David the seventh…
[David the seventh] Question: How is it that only seven sons of Jesse are here listed, and among them David as the seventh, when it is said in 1 Samuel 16; 17 that Jesse had eight sons (Estius)? Responses: 1. Jesse had seven natural sons of his own, and one adopted son, namely, Jonathan the son of Shimea, 2 Samuel 21:21 (Hebrews in Estius, Rupertus in Tirinus). 2. Or perhaps of the eight sons one was taken away by a premature death (Tirinus), before David came to the kingdom, 1 Samuel 16:10 (Grotius).
The seventh: For though he had eight sons, 1 Samuel 16:10, one of them either died presently after that time, or is neglected for some reason now unknown, as others are. See the notes on Matthew 1:8, 9.
Verse 16: Whose sisters were Zeruiah, and Abigail. (2 Sam. 2:18) And the sons of Zeruiah; Abishai, and Joab, and Asahel, three.
[The sons of Zeruiah, etc.] They are not called this just one time, but the name of the father is never set forth. Evidently they were more illustrious by their maternal family, than by their paternal side (Menochius).
[Abishai, Joab] Hence it is evident that Abishai was older than Joab (Mariana, similarly Lapide).
[Jether the Ishmeelite] In 2 Samuel 17:25 the same is called an Israelite. Responses: 1. He was by residence an Ishmaelite, not by race (Mariana). He lived among the Ishmaelites for some time (Menochius out of Lyra), just as Elimelech did in the land of Moab, Ruth 1 (Lyra). 2. Or, he was of the family of Ishmael, but a Hebrew by religion (Menochius out of Lyra).
The Ishmeelite, by birth or habitation, but by profession an Israelite, 2 Samuel 17:25, where see my notes.
 Hebrew: וְאִישַׁ֛י הוֹלִ֥יד אֶת־בְּכֹר֖וֹ אֶת־אֱלִיאָ֑ב וַאֲבִינָדָב֙ הַשֵּׁנִ֔י וְשִׁמְעָ֖א הַשְּׁלִישִֽׁי׃  1 Samuel 16:9: “Then Jesse made Shammah (שַׁמָּה) to pass by. And he said, Neither hath the LORD chosen this.”  1 Chronicles 27:18: “Of Judah, Elihu (אֱלִיהוּ), one of the brethren of David: of Issachar, Omri the son of Michael…”  Hebrew: נְתַנְאֵל֙ הָֽרְבִיעִ֔י רַדַּ֖י הַחֲמִישִֽׁי׃  Hebrew: אֹ֚צֶם הַשִּׁשִּׁ֔י דָּוִ֖יד הַשְּׁבִעִֽי׃  Rupertus (1091-1135) was a learned Benedictine, Abbot of Tuits on the Rhine.  Hebrew: וְאַחְיֹתֵיהֶ֖ם צְרוּיָ֣ה וַאֲבִיגָ֑יִל וּבְנֵ֣י צְרוּיָ֗ה אַבְשַׁ֛י וְיוֹאָ֥ב וַעֲשָׂה־אֵ֖ל שְׁלֹשָֽׁה׃  Hebrew: וַאֲבִיגַ֕יִל יָלְדָ֖ה אֶת־עֲמָשָׂ֑א וַאֲבִ֣י עֲמָשָׂ֔א יֶ֖תֶר הַיִּשְׁמְעֵאלִֽי׃  2 Samuel 17:25: “And Absalom made Amasa captain of the host instead of Joab: which Amasa was a man’s son, whose name was Ithra an Israelite (יִתְרָ֣א הַיִּשְׂרְאֵלִ֔י), that went in to Abigail the daughter of Nahash, sister to Zeruiah Joab’s mother.”