At A Bear's Mercy — Caitlin Ricci

Pierce Nillian is shy, socially awkward, and hasn't had a real date in years. At least not one that wasn't with someone from one of his therapy groups. When he meets a man needing help with an injured dog, Pierce knows how to help. He's a marine biologist who works with animals all day, and also has two dogs of his own. Once the dog is patched up, he expects not to see Tim again.

But the next day Tim comes back, and this time he's brought reinforcements in the form of his sister, along with Pierce's little sister, who it turns out are dating each other. To add to it, Nikki and Jo can't be together officially until Tim finds a mate, because Nikki and Tim are bear shifters. Pierce has done a lot of things for his sister in the past, but becoming a bear's mate is a tall order. His gut reaction is to refuse, but Tim is good at getting his way, and he wants Pierce for himself.