The Family Tree is a visual representation of the web of character relationships within your faction, and offers the functionality for you to interact with those characters and generate Intrigues, which bring new gameplay options. The characters in your faction can forge strong bonds and alliances with other factions. Marriages can produce offspring, who grow and obtain duties of their own. Characters are born, live their lives, and eventually die throughout the course of a game.
To learn more about the Family Tree as part of the Ancestral Update please visit the FAQ https://www.totalwar.com/blog/total-war-rome-ii-ancestral-update