John Gill Commentary Nehemiah 12:9

"Also Bakbukiah and Unno, their brethren, were over against them according to their offices." — Nehemiah 12:9 (ASV)

Also Bakbukiah and Unni
Two other Levites; the first is mentioned in (Nehemiah 11:17) ,

their brethren, were over against them in the watches ;
the Levites were divided into twenty four wards, and these were placed one against another, (1 Chronicles 23:6) (26:12) .