Brother of song = singer, the officer who was “over the household” of Solomon (1 Kings 4:6).
Ahishar
1 verse
1 Kings
1 Kings 4:6
And Ahishar was over the household: and Adoniram the son of Abda was over the tribute.
From Easton's Bible Dictionary
Matthew George Easton, 1897
From Smith's Bible Dictionary
William Smith, 1884
the controller of Solomon’s household. (1 Kings 4:6)