In my mind, I think that the best way to describe multiple characters in one paragraph is to find a theme or a character trait that encompasses all of them. This can be used to construct a paragraph that uses all of the characters as a central tenet to unify them in the paragraph. For example, if your paragraph was to focus on how the character trait of determination is evident in Hillenbrand's characters, I think you can talk about how Louie demonstrated determination in his time in the war and in seeking to piece together his life after it. The grit and focus required for running is evident in his characterization throughout the work. This same determination is evident in Phil throughout the war and in his time as a Prisoner of War. Determination is also evident in the sadism of Watanabe, determined to inflict as much pain and brutality in the name of country and war as possible. Finally, determination can be seen in Cynthia, who feels committed to seeking to give the marriage to Louie another opportunity in the face of Louie's determination to change his life. This can be done for as many characters as possible. The development of the paragraph is able to be accomplished when the focus is themes or traits that multiple characters represent or embody.