Whoever they are, they're clearly after Wit, and they feel that getting to Nomad/Sigzil/Aux will help them get to Wit.
But is it possible that the Night Brigade is a benevolent group? Obviously the name sounds ominous, but that's based on humanities predisposition to night time on earth. Things are vastly different in the Cosmere, eh?
A branch thought off of this...Nomad says to Wit that if he stays, the Night Brigade will catch up to him, then use him to trace the Dawnshard back to Wit...so my secondary question....did Wit and Sigzil hold the same Dawnshard?
So, sooo looking forward to these books!