Complex sentence: The bomb failed to detonate, allowing Diem to run to the eastern wing and down a flight of stairs to the cellar, along with his elder brother Archbishop Ngo Dinh Thuc, younger brother Ngo Dinh Nhu, Madame Ngo Dinh Nhu and their children.
Split into simpler sentences: The bomb failed to detonate, allowing Diem to run to the eastern wing to shelter in its cellar. He was joined there by his elder brother Archbishop Ngo Dinh Thuc, younger brother Ngo Dinh Nhu, Madame Ngo Dinh Nhu and their children.