What book has a boy in a military world that has a parallel world?

It's about a boy that has an overly religious brother named Sterling (i think) but he live in a world where he has to go to military school. His brother, whom he adores, dies of yellow fever right after he got the cure and he reads a book his father or grandfather wrote, that is illegal, that was a prophecy about the prince that went missing. It also has chapters that go on the prince in the parallel world.What book has a boy in a military world that has a parallel world?Sounds like you are talking about "The Eyes of a King: The Last Descendants #1". It's a trilogy.