The Dark Will Rise by Michaela Haze

Cruinn is in turmoil.
Scattered, the five creeds of the lake pull together to try and rebuild, unsure if the war is over or has only just begun.
Maeve and her princelings must agree about the future of the Twilight Lake, which means meetings, politics, and dealing with the same courtiers that made Maeve’s childhood a living hell.
As Maeve and the princelings lead their respective kingdoms, they must also navigate the bonds that start to form between them. Can love blossom from a predestined path, or will they struggle against the shackles of Shíorghrá? As word reaches Cruinn that the Siren Queen intends to collect on her uncle’s debt, Maeve is out of her depth even after King Irvine has turned to foam.
The prophecy calls for all five creeds to join together. Shay Mac Eoin of the Nymphs proves more important than anyone could have ever known, and his impending nuptials might inspire another war.
It shouldn’t have been easier when everyone was killing each other.