BattleTech: Iron Dawn (The Rogue Academy Trilogy, Book One) - BattleTech YA

GHOSTS IN THE DARK. Jasper and Nadine Roux are cadets at the Ritza MechWarrior Academy; a dream come true for the orphaned siblings from the war-torn planet of Hoff. For the last six years, Emporia has been their home. Sponsored to the academy by the powerful Vogel House, both cadets are expected to excel in all tasks. Their dream becomes a nightmare when the Draconis Combine lands at their doorstep. It's up to the siblings to stop a renegade Seventh Ghost Regiment warlord when he lays claim to a piece of the Inner Sphere-starting with the Federated Suns' planet of Emporia.
The border world looks like easy prey, but this warrior of the Dragon is about to learn how wrong he is. After the few MechWarriors on the planet are taken hostage, the Sponsored and Blooded cadets of the Ritza Academy fight like they have nothing left to lose.  It's a fight that will cost them more than they know...