Several of the characters in The Silver Sword are family members or on friendly terms but are separated by events, which result in tremendous in difficulties. Therefore, it would be logical for them to write to each other. However, for most characters, the chief difficulty is that they have been forcibly separated and do not know the whereabouts of their relatives, and they sometimes later lose track of even more family members. Because of those circumstances, a letter would be more like a diary entry, as they would not have an address of where to send it.
Joseph, the father in the Balicki family, is a schoolteacher and administrator, so writing would be an expected form of expression for him. After he is arrested and taken away, he loses touch with his wife and children. In the prison camp, when he is ill, if he had enough strength he might consider writing a journal-type letter as a way to fill his time and share his thoughts with his family.
On the children’s side of the Balicki family, Ruth is a likely letter writer. Although separated from much of her family, she remains emotionally close to them. She later becomes a teacher and continues to search for her missing parents. As an educated person, she would be a good writer who could conceivably write a journal-type letter from her to her parents. This could include descriptions of her and her siblings's survival and her concern when Edek disappears.