Morgan by Nia Farrell

When grad student Morgan Leviss chose sexual surrogacy for her thesis, she never expected to become one. Now she’s tasked with turning two reclusive men into social creatures. Zac Blackstone and Aiden Goldman are nothing like what she expects. Handsome and charming, they’re a puzzle she finds intriguing.
Zac and Aiden have known each other for over two hundred years. Part of a cadre of shifters, they’re on a mission to mate and procreate. Powerful warriors for centuries, they lack the social skills and sexual experience needed to attract a partner. When a beautiful redhead comes into their life to teach them, they discover new hope.
Bound by secrecy, the men can’t tell her who they really are. What they are. Increasingly drawn to Morgan, they begin to recognize her as their fated female. Convincing her that she’s theirs may be as hard as keeping her alive when danger appears from the shadows.