Your Sister's Sister, released in 2012, is a very watchable film, though not unduly mentally challenging. The plot can be summed up very simply. Jack is in love with Iris, but sleeps with her sister Hannah, a lesbian with her own personal agenda. That's about it really as the rest of the film is almost exclusively about the relationships between these three which are complex given what has happened. Alright, perhaps there is a little more to it than that, but that is the basic bones of the film and the rest is really setting the scene and adding the flesh to the bones.
Although not overly complicated, this is a film which holds the interest and the interaction between the main characters is sometimes poignant and often humorous, since each has their own personal issues to deal with. This film is all about the three main characters who are very well cast in their roles. I thought Emily Blunt of Salmon Fishing in the Yemen fame, did particularly well as iris, although Mark Duplass and Rosemarie DeWitt also put up creditable performances.
This is not a film which has much action, but is all about people dealing with, and coming to terms with difficult situations and finding common ground. This is a film which has been well directed and the subject matter treated sensitively. Probably not the most memorable film you are going to watch this year, but certainly reasonable entertainment.