Our Vast and Yearning Ends by Val Saintcrowe

Having survived one attack on their lives, the Night King and Sun Queen shouldn’t be surprised when another attempt is made. But they are.
In the Eeslia, Larent, Onivia, Cassus, and Isha are halted at the entrance to the Cyria villa by fae guards, who claim that their leader, a powerful woman with magic, must grant them entry. No one is more surprised than Onivia to discover this powerful woman is her estranged Aunt Toria.
In the north, Albus’s and Galvina’s domestic retreat is shattered by the arrival of Renccius, Albus’s friend and sometime lover, who comes from Albus’s brother Magnerius with an offer. Magnerius is making a bid for power. He wants to wrest the Vostrian empire back from the fae.