The Dhulyn and Parno Novels: Volume One by Violette Malan.

Dhulyn Wolfshead and Parno Lionsmane are members of the Mercenary Guild, veterans of numerous battles and missions, and masters of martial arts. But more than that, Dhulyn and Parno are Partners, a Mercenary bond that can only be broken by death. And though one’s past is supposed to be irrelevant to a Mercenary Brother, who they’d been might make the difference between success and failure in their missions.