Complex sentence: He married Margaret Fastoe in 1964; they had two sons and daughter, Hattie, who at the time of her father's death had just published a memoir of Gareth, her brother, who had committed suicide in 1994 at the age of 24.
Split into simpler sentences: He married Margaret Fastoe in 1964; they had two sons and daughter. His daughter Hattie had, at the time of her father's death, just published a memoir of her brother Gareth, who had committed suicide in 1994 at the age of 24.