In "The Soldier's Home," what are the reasons for Kreb's connection to his sister Helen and his distance from his mother and father?

Harold has an easy relationship with his sister Helen. He calls her "his best sister" and says he likes her. Helen is warm and affectionate with Harold; she teases him, makes no difficult demands on him, and does not judge him or his behavior once he has come home. She accepts him as he is and is simply glad for his company. Harold's mother and father, however, watch his every move and treat him as the boy he once was. Harold will be allowed to drive the family car, and he should not "muss up" the morning newspaper. His parents make demands on Harold that he is not yet able to meet. They think it is time for him to settle down, get a job, and get on with his life. They have no understanding of what has happened to their son in the war--nor do they really want to know.