The Brothers Rule by Carolyn Faulkner

When Jace Rule first told his brothers, Adam and Ryan, about the girl he was dating, they couldn’t believe their ears. Laurie had been dating the three oldest brothers at the same time and hadn’t even realized it.
When Jace tells Laurie, she is flabbergasted, but together, they soon decide that she’ll continue to see all three of them until she can decide between them.
When that turns out to be an impossible decision, their younger brother, Nick, who is a lawyer, suggests that a contract between Laurie and the three oldest Rule brothers might be the solution.
But can that really work, being in an arrangement with three virile, dominant brothers? They’ll soon find out.

Publisher’s Note: This reverse harem contains steamy scenes as well as a theme of power exchange.