A Reaper at the Gates (An Ember in the Ashes #3) by Sabaa Tahir

Synopsis: Finally reunited with her brother, Laia has been tasked with stopping the Nightbringer, the king of jinn. Elias has to adapt to his new role of Soul Catcher and the responsibilities that come with that role. Helene must try to stay true to the Emperor's wishes, as well as protecting the only family she has left.