I need references about Michael Corleone's character and his changes of attitude towards family business in The Godfather.
His "characters"? I believe you mean his character. Michael initially feels at least a distance and at most a degree of shame over the manner that his family conducts its business. Over time and through the attacks the family endures, Michael's feelings change and his moral absolute point of reference becomes more pragmatic and relativistic. His time in Sicily allows him to born again into his family heritage and the struggles they have overcome.