Review: 'Your Sister's Sister' has charm Truly, madly, deeply affable, Mark Duplass has officially blown up real good. The filmmaker and increasingly busy actor has two new movies out recently, the mainstream-y festival successes"Safety Not Guaranteed" and writer-director Lynn Shelton's"Your Sister's Sister." Some performers, even relatively young ones, have the knack of being easy company, handling various assignments without breaking a sweat. I don't know how versatile Duplass is, yet, but what he's been asked to do he does well. Shelton's previous feature was "Humpday," which also costarred Duplass, and in that picture two hetero pals took it upon themselves to make a gay porno film on a dare. Graced with a similar delicacy of touch, nagged by some of the same ambling frustrations, "Your Sister's Sister" deals with another awkwardly ticklish situation. After giving a misjudged and hostile toast at a gathering in honor of the one-year anniversary of his brother's death, Jack (Duplass) is packed off by the late brother's ex, played by Emily Blunt, to her family's secluded island cabin. He needs to be alone, she reasons. But he's not: Iris' half sister, Hannah (Rosemarie DeWitt) has gotten there first, nursing her own heartbreak over the end of a seven-year relationship. Bisexual, but lately lesbian, Hannah has a tad too much tequila with Jack on their first night as housemates. Suddenly, they're in bed. Just as suddenly they're engaged in several seconds of the least romantic intercourse two drunken mismatches can have. Then Iris arrives unannounced, and there's a secret to keep. While "Your Sister's Sister" sounds like the stuff of high-pressure romantic comedy, Shelton's naturalistic approach to storytelling keeps the developments as honest as possible. It's pleasant as far as it goes. For all the blithe interaction among the central three performers, however, the material's conventional and predictable. Hannah's a vegan, which appalls Iris and Jack; in Seattle, this is a big deal? Jack is really only a sketch of a man, a character admittedly who is meant to be half-formed and stuck. Duplass does all he can to find someone in there. The best exchanges belong to DeWitt and Blunt, who share a lovely directness and quicksilver emotional quality. The best five minutes of "Your Sister's Sister" can be found in a late-night conversation in whispers between Iris and Hannah. While Hannah dances around the secret she's keeping, something truer emerges: the feeling these two sibs have for each other, even at a remove. Shelton has considerable talent. With luck, her next film will challenge her to dig deeper, push harder, risk some serious ambiguity. The charm's there already.