Kel might think he's helping Esme. But just about everything he does seems designed to weaken her. Killing the priestess is what ultimately tips the mob against Esme. More than anything, the voice seems to be pushing Yatwer's agenda -- returning the empire to the disenfranchised.
re: Maitha suspecting Kel, the WLW scene with Inrilatas, Maitha and Kel confirms that he is genuinely in the dark about what's going on.