Valley of the Bear Kings Series by Rowan Stone

Eirik concealed his omega nature his entire life, fearing to be outcast from his service to the gods if his secret was discovered, but the Bear Kings uncover the truth within moments. Confronted by King Valdymir's lust and his own secret needs, Eirik surrenders himself to the Bear King's primal passion and his own yearning for the bear's offspring...

Captured along with the other humans who have invaded the Bear Kings' sacred valley, the thrall Sivard fears a dire fate. Instead, he is claimed by the golden-furred Bear King Hallthor, who reveals Sivard's true omega nature and awakens passions the human has never before experienced. Eager to serve his new king's most primal desires, Sivard surrenders himself fully, and soon finds himself filled to bursting with the mighty king's potent seed.