Scarlett Johansson and Sienna Miller play sisters in Kristin Scott Thomas’s directorial debut, which the actor dedicates to her two fathers.

Thomas co-wrote the script with her husband, journalist John Micklethwait, which includes a particularly poignant monologue for her character telling her daughters, essentially, to grow up and move on — a mature and worthy statement that might come a bit too late. “My Mother’s Wedding” feels only partially realized.