Amasa captain of the host - From the account in this verse, it appears that Joab and Amasa were sisters' children, and both nephews to David.
Ithra an Israelite - Or “Jether the Ishmeelite” 1 Chronicles 2:17. “Ithra” and “Jether” are practically the same names. “Israelite” in the text is wrong. It should be either “Ishmaelite” or “Jezreelite” 2 Samuel 3:2.
Abigail the daughter of Nahash - If Zeruiah and Abigail were Jesse‘s daughters, the only probable way of reconciling our text with 1 Chronicles 2:16-17, is to suppose that Nahash was Jesse‘s wife. If Zeruiah and Abigail were only sisters of David by the mother, then Nahash might be the name of her first husband.