Complex sentence: They had two sons, George Newhall Clark (1887-1906), who died while at Harvard of influenza, and Sydney Procter Clark; and two daughters, Frances Clark Stoddard, and Christine Clark Willetts.
Split into simpler sentences: They had two sons, George Newhall Clark (1887-1906), who died while at Harvard of influenza, and Sydney Procter Clark. They also had two daughters, Frances Clark Stoddard, and Christine Clark Willetts.