This book is replete with examples of these three characters showing love, solidarity and concern to their family members. The book is an amazing and touching example of how close a family can be to one another, close to the point of being willing to sacrifice one's life in order to help a family member.
Everything that Jeremiah does is for his family. For example, he takes Reuben and Swede on the spontaneous cross-country trip in an attempt to find Davy and try to warn him of the authorities that are trying to find him. That is a risky endeavor, but he did it because he loved his family and his son. Another example is how he works at his rather lack-luster job of being a school janitor; probably not his life ambition, but one that can feed the children. And lastly, he gives his life for his son, Reuben.
Reuben does his best to testify well at Davy's trial, even though it ends up not going well. He also sneaks off to find Davy and spend time with them in the snow-covered tundra where they catch up with him. He also spends countless hours with Swede, encouraging her to write and listening to her stories, which are a sort of therapy for her and the family.
Swede is a plucky girl who tries her best to take over the role her mother left. One way she shows love is to use her money and resources to buy food for the starving family, and fix them a nice meal. She also tries to make Davy out to be a sort of hero in her western poem, which shows her love for her brother. In addition, Swede encourages her father's romance with Roxanne, a way to show her father that happiness can be his.
I hope that those examples helped; good luck!