The answer is: Zeruiah and Abigail

1 Chr 2:16

David, famous for his harp, sling, and the monumental tales of his reign, also had a fascinating family tree! He had two prominent sisters mentioned in the Bible: Zeruiah and Abigail. Zeruiah was actually the mother of three courageous warriors who served under David – Joab, Abishai, and Asahel. This makes her quite an important figure in David's military successes!

You might find it interesting that Zeruiah's sons played pivotal roles during some of the tumultuous times of David’s kingship. For instance, Joab, her most notable son, was both a devoted general and later a controversial figure who navigated the tricky waters of loyalty and betrayal.

Abigail, on the other hand, has a rich story of her own. She started as the wife of a rough man named Nabal, but after Nabal's death, she married David. Known for her wisdom and acting as a peacemaker, Abigail is often celebrated for her quick thinking that saved David from making a rash decision in a confrontation with Nabal.

Besides their personal stories, these sisters remind readers that David's reign was also about family networks and alliances, which were crucial in the turbulent times of ancient Israel. Which makes one ponder about the dynamic relationships we see in families today – in whatever context, they often shape who we are! So, while David might have been a giant-slayer, his sisters also shaped the history of Israel in less flashy but equally crucial ways.