The pronoun them
refers to the nobles and officials
who had wronged their brothers. Over against this (relatively small) group Nehemiah positioned a great assembly
of the remaining population; this would include so many of the people voicing the outcry
of Nehemiah 5:1 against these very men. Nehemiah then speaks the words of Nehemiah 5:8 to these nobles and officials in the hearing of the great assembly.
Clearly, the work on the wall came to an abrupt halt for the sake of this meeting!
7 I took counsel with myself, and I brought charges against the nobles and the officials. I said to them, “You are exacting interest, each from his brother.” And I held a great assembly against them