The Wayward Sons & the Seattle Sirens by A. Winchester

To save one…
After a desperate plea for help from his sister, Ryder Collins and Grayson Harper hit the road. With Seattle looming in their sights, both men are aware of the dangers that lurk in the shadows—and not just the siren they’re hunting. To keep Ryder safe, Gray must take this demon on alone.
When the hunt takes an unexpected turn, Gray goes missing. Ryder finds himself in a race against the clock to save the man he loves. In the heart of the siren’s den, he’ll do whatever it takes, even if it costs him his life.
… the other is willing to give up everything