Symbolism, Imagery, Allegory
Matthew, Callie, and Emmy have grown up in the same house all of their lives. That's because it's a house that's been passed down through their family, and now it's co-owned by Nikki and her sister, Aunt Bobbie. Because they both own it, the sisters have split up the house so that they live in separate apartments.
This separation represents their emotional distance from each other as well. Aunt Bobbie stays in her side of the apartment and doesn't venture into Nikki's domain, even when she knows that the kids might be abused or neglected. She feels like it's not her place to walk into Nikki's part of the house and intervene.
But when Aunt Bobbie realizes that it is her job as an adult to keep the kids safe, the separation within the house becomes a little blurrier. When Nikki goes to jail for a few days during Christmas break, Aunt Bobbie breaks down the barriers in the house:
The doors of Aunt Bobbie's apartment, and of ours, were thrown open, and the two floors felt like one big space, one big house. The college kids who rented the first-floor apartment had all left for the holidays, and so we felt completely free in that house in a way we never had before. (35.3)
The breaking down of the physical barriers in the house is mirrored by the breaking down of emotional barriers between Aunt Bobbie and the children. When she starts to open up her apartment to them, she becomes a guardian figure and someone that the kids can rely on for help—as well as for shelter. Her home is on its way to becoming theirs, too.