Blood Bound by Odessa Hywell

Marcus Malnar—head asshole of the Malnar Family—has spent a lifetime stepping over the bloody remains of his enemies. Fulfilling his purpose is the only thing that matters; nothing can stand between him and his goals. Except his nephew.
Despite what everyone says, Holden Malnar isn’t spoiled. If you ask him. He’s a pint-sized bundle of insanity with a pain kink, barely held together by a straitjacket, and he owes everything to his uncle. There’s no limit to what he’s willing to do for the man. No. Limit.
Loyalty means everything. Betrayal is a bitter pill to swallow. When Marcus and Holden have to rely on one another to weed out the traitor attempting to destroy their Family, there is no fighting the inevitable.