The term has a variety of meanings, ranging from literal brothers in the flesh to various non-family relationships (2 Samuel 1:26). In the present context, the term most naturally refers to Sanballat’s allies, persons who would share his disdain for the Jews (and so possibly agree that Jerusalem’s reconstruction project represented a threat).
2 And he said in the presence of his brothers and of the army of Samaria, “What are these feeble Jews doing? Will they restore it for themselves? Will they sacrifice? Will they finish up in a day? Will they revive the stones out of the heaps of rubbish, and burned ones at that?”