Emily Blunt has quite the sister act going this year: In next week's The Five-Year Engagement, her closest confidante is sibling Alison Brie, while Your Sister's Sister (due June 15 from IFC Films) puts Blunt and sister Rosemarie DeWitt in close quarters with Mark Duplass and builds an unlikely love triangle. You see, Blunt has a crush on Duplass that she's kept secret since his brother's death, and she suggests that Duplass take some time off for a remote vacation at her family cabin, which she'll then crash. Only problem is, once Blunt gets there, she finds that DeWitt decided to use the cabin, too ... and Duplass and her sister are navigating an awkward morning after their own secret hookup. The Lynn Shelton–directed Sister has already played film festivals at Toronto and Sundance, and we found it charming each time; Yahoo debuted the trailer today, while Vulture's got the film's exclusive poster. Enjoy!