Who is Ngo Dinh Diem, Ngo Dinh Nhu, and Ngo Dinh Can from The Tears of Autumn and what is their importance?

These are historical figures, Diem is the autocratic President of South Vietnam overthrown by generals on 2 Nov 1963, and Nhu is his younger brother and principal advisor. Both are shot in the head sitting in an army vehicle, ostensibly by a Vietnamese officer. A third brother, Ngo Dinh Can, seeks asylum from the Americans but is turned over to South Vietnam, imprisoned, and expected to be executed. The brothers have their horoscopes prepared and, seeing clearly that their days are numbered, begin making arrangements to "spit out of their graves" at the Americans. This is Operation "Lê Thu." Diem's lucky number is seven, and John F. Kennedy's assassination is arranged 21 days (three times seven) after Diem's death. Twenty-one is also an important day in Vietnamese funereal rites.