The original question had to be edited down.  One significant connection that Robert has towards his sister is the demonstration of a universalized notion of love which exists between himself and animals.  When Rowena dies and her rabbits are ordered to be killed by their mother, Robert displays a connection with her in his unwillingness to stand by to such cruelty.  Robert's desire to leave reflects how much love he holds towards living creatures.  In the savagery of war, Robert's connection with his sister underscores his participation in the war.  He operates on the level of curating life in all of its forms.  Robert seeks to maximize the spirit of life that exists in both animals and humans.  This is rooted from his relationship with his sister.  The relationship that Robert shares with his sister is one that highlights his desire to maintain life.  The guilt and feelings of imprisonment that he feels when both his sister and her rabbits die help to motivate him throughout the work.

The bond that both share is relevant throughout the narrative.  One sees this at the end when Robert saves the lives of both humans and animals in one of his final acts of the war.  Robert's bond with his sister is what enables him to act in the interests of all life.  Robert comes to see life as an extension of his sister, reflective of what he believed in terms of the relationship he had with his sister.  Rowena's spirit lingers in Robert after her death.  As the complexities of being in the world present themselves, Robert finds himself struggling to find answers to intricate questions.  The one certainty with which he operates is that life in all of its forms is something to be preserved at all possible costs.