Kiss of Iron by Leigh Kelsey

Nothing cuts as deep as a fated mate bond.
Maia has found her mates, only for one to betray her. Once again at the mercy of her aunt, the cruel queen of the fae court, Maia will have to draw on her new, volatile magic and beg the saints for help. Because Ismene will stop at nothing to make her obey. She has wicked plans for Maia’s snaresong power, and not even Ark, the palace guard who might be Maia’s mate, can protect her.
A dark war rises.
Dangerous evil festers in the City of Skies, and though Azrail and his rebels have rescued the missing beastkind, the atrocities won’t stop. Dark forces are gathering across the Vassal Empire, threatening every realm in the Saintlands, and as Maia’s mates fight to save their tortured princess, it’s clear the evil is only beginning.
The worst is yet to come.