Empire of Bones by Terry Mixon

The Terran Empire is dead. Long live the Empire!

Commander Jared Mertz, the bastard son of the emperor, and his half-sister, Princess Kelsey, barely speak to one another. To their dismay, their father seizes an opportunity to change that and sends them on a dangerous quest to explore the fallen Empire.

Separated from home by an impassable gulf and struggling to redefine their relationship, they find themselves thrust into a vicious war. Unless they work together to stop the Empire’s deadly legacy, billions face a horrific fate.