The Emperor's Blades (Chronicle of the Unhewn Throne Book 1) by Brian Staveley

Set in a sprawling epic fantasy world, the story follows three siblings whose lives are torn apart after the mysterious assassination of their father, the Emperor. Valyn trains among the lethal elite Flayed Wings, Kaden studies the deep arts of mind and spirit in a remote mountain monastery, and Adare navigates the treacherous politics of the capital. Together, they must uncover the conspiracy behind the throne before their empire collapses into total ruin.