We know that David, the King, had six brothers and two sisters. His sister, Zeruiah, was mother to three sons, Abishai, Asahel, and Joab, all of whom found service in David's military machine.
In conflict with Ishbosheth's Israel, David's army defeated the foe, but Abner, leader of Ishbosheth's forces, fled on foot. Asahel, noted for fleetness of foot, if not for prudence, chased after Abner. Abner called to him to stop, averring that he did not wish to kill him, but Asahel persisted, and Abner did indeed slay him.
Abishai stood with David before David was king, for it was he who with David sneaked up on the sleeping King Saul and stole his spear and water flask. Much later Abishai was noted to have slain three hundred men in battle.
The most famous of the brothers was Joab, and we look briefly at the record of his service to his uncle, the king. Joab rose to the position of General of the Armies, and as such he was a trusted advisor to the monarch. Joab's loyalty to Uncle David might well be illustrated by his role in the plot of David to make a widow of Bathsheba, who, as we know, later became the mother of the future king, Solomon.
Let us note here that notwithstanding Joab's forgiveness of Abner for the killing of Asahel, he did ultimately slay Abner, much against the wishes of the king. Strike one. Nevertheless, Joab's leadership was invaluable and he continued to rise in the esteem of all, and he had the ear of the king. One bit of counsel he gave, though, that the king rejected was the advice to David, "Do not this thing" in reference to the king's command to enumerate the people. Failure to heed this advice came back to bite David.
During Absalom's revolt, Absalom appointed Amasa leader of his forces. This Amasa, apparently a cousin of Joab, reaffirmed his loyalty to David, but was later murdered in a ghastly manner by Joab during the pursuit of Sheba who was attempting to lead the Israelites in revolt. Though Joab successfully squelched the uprising, this is strike two.
The account of Joab's deeds is contained largely in the Second Book of Samuel. We turn to the First Book of Kings, chapter two, to discover Joab's ultimate reward for his decades of service.
In his charge to his successor, Solomon, David said, You know Joab slew Abner and Amasa. Do according to your wisdom. Do not let his head go to the grave in peace.
Joab offered his allegiance to Adonijah, Solomon's elder brother. Strike three.
Solomon followed his father's counsel.