The Company You Keep (BDSM Multiple Partner Romance) (Ghost Seekers Series, Book Six) by Melinda Barron

Twin brothers Jesse and Josiah Jackmon have been faithful members of the ghost seekers for years. They have also guarded a book written by a warlock in the fifth century meant to use mortal women to bear the warlock children.

Shopkeeper Jesse knows the book has to be kept secret, but lately there has been a great deal of interest in the book, including from two beautiful fairies, Luna and Sebille, who want to take the tome for themselves.

Soon, Jesse realizes that everything isn't always what it seems, and you have to learn to trust people, no matter how long you've known them.