What are the motifs in Between Shades of Gray by Ruta Sepetys?

The importance of family is a recurring idea. Those who are arrested go to great lengths to find news of their families' whereabouts and conditions. This is seen early on when Lina leaves the train with Andrius in search of her father. She is in danger but goes anyway. The desire to stay in contact is seen later when the people put themselves in danger in order to send letters that may not ever reach their destinations.