The Unbreakable Crown by Carina Finn(Feast and Famine #2)

The magic and adventure continue in the second book from the New York Times bestselling Feast and Famine series, as heirs of the two houses must survive the trials at a boarding school for demons if they are to return home to the land of Fauret.

Abundance Feast excels at throwing parties, assembling fashionable outfits, and being polite. Prophecies have always been for her sister, Merri, heir of House Feast. Besides, Bun doesn't know magic like her sister. So she's not prepared to be part of the Eternal Three, let alone trapped in the demon realm with Merri, Rue, Wort, and Sage.

Wort Erebos grew up in the woods with his father and little sister. Their life was magical in its own way, but their focus was on survival. In Demonspace, Wort discovers the Erebos family has a long heritage that his father has kept secret...but why? And at what cost? And how can Wort trust the very people who lied to him?

Merri and Rue are anxious to return home to their guardian duties in Fauret, but the pathway between realms is damaged. The only hope of returning is by gaining access to the ancient library at Tenebrun, the magical boarding school for the elite of this world. Merri and Rue spent their lives training for their guardianship duel. How will Bun and Wort survive these Tenebrun trials?