Lilly by Skye Jones

When a lonely young woman finds that she’s destined to be the mate of two ancient and battle hardened dragons, life as she knows it is about to change.
Lilly has led an opulent but lonely life with her wealthy adopted parents. She’s never really fit into their world. She finds out why when her biological sister comes looking for her, telling her she’s not quite human. When Lilly meets two huge and ancient dragon shifters who claim she is theirs, she runs scared.
Rhyndor is one of only a few warrior dragons left who have survived centuries on earth. He’s battle-scarred, and full of guilt about something he did many years ago. He’s alive but not living. Drifting through the world on autopilot; until he meets Lilly. She re-awakens the protector within, and he must have her.
Callum is about to get everything he wants. The female he craves is within their grasp, and even better, she’s brought out the warrior spirit within his bonded male, Rhyndor. But then she runs from them, and Rhyndor gets the crazy idea he needs to atone for his sins.
Instead of getting everything he wants, Callum might be about to lose it all.
Lilly is book three of the Dragon Clan series, but can be read as a stand alone novel.