David, Zadok (a descendant of Eleazar), and Ahimelech (a descendant of Ithamar) divided them into groups to carry out their assigned responsibilities. ¹ 

Jahath was the oldest and Zizah the second oldest. Jeush and Beriah did not have many sons, so they were considered one family with one responsibility.

This was the order in which they carried out their assigned responsibilities when they entered the Lord’s temple, according to the regulations given them by their ancestor ¹  Aaron, just as the Lord God of Israel had instructed him. ² 

As for the Hebronites: Hashabiah and his relatives, 1,700 respected men, were assigned responsibilities in Israel west of the Jordan; they did the Lord’s work and the king’s service.