Miecze Cesarza by Brian Staveley

Set in a richly detailed fantasy world, the story follows the lives of three siblings, each grappling with their own challenges after the assassination of their father, the Emperor. The eldest son, Kaden, is training in a remote monastery to master ancient powers, while his brother, Valyn, endures brutal military training to become an elite soldier. Meanwhile, their sister, Adare, navigates the treacherous political landscape of the empire's capital. As they uncover hidden threats and dark conspiracies, the siblings must confront their destinies and the forces that seek to tear their family apart.