Krakauer and others have speculated that McCandless was estranged from his family because of his relationship with his father. What was his family life like? Does it explain his later behavior?

I don't think Chris' family life fully explains his behavior. Chris was upset when he discovered his father was having an affair, which helps us to understand the animosity he had towards his father. What it doesn't explain, however, is the complete separation from his family. Chris was indeniably close to his sister, but even the few post cards he sent her eventually stop.