The Seattle International Film Festival, the nation’s largest, has announced it will open with Your Sister’s Sister at a May 17. Pic marks the first locally-produced and shot film to open the fest in its 38-year history. Directed by Lynn Shelton, one of Variety’s 10 directors to watch, “Your Sister’s Sister” revolves around three young people after a drunken night at a remote cabin in the Pacific Northwest. IFC Films acquired the pic after its Toronto premiere. “Lynn Shelton has made a pitch-perfect comedy of errors, infused with the right balance of humor and pathos that I absolutely love,” said SIFF artistic director Carl Spence.