I'm starting to think that Oathbringer is written by Shallan. I think that with these multiple personalities that she is creating and the fact that she will still be working with the Ghostbloods in some capacity that she will do something major in this book that really undercuts the rest of the protagonists and put her on the outs for a while. When I read the Epigraphs for the last couple releases it made me think of Shallan finally telling Adolin what happened in her childhood.
I also think that the second murder was conducted by the Ghostbloods and they will reveal themselves to Shallan as the one who did it and also that Adolin killed Sadeas and use that to coerce her to help them in their game.