The Jangovar are working the other Easterlings to the bone.
'You, Chayasír. Get those laggards back to work. I do not care how, whip them if you must! The dwarves will be upon us any day and we must be prepared!'
Shackled Easterlings can be found inside Utterby.
You should secretly loosen the shackles of these Easterlings.