Complex sentence: He is the son of the late playwright Michael Cook and playwright and actress Janis Spence, has an older sister named Sarah, a younger sister named Perdita, and a younger brother Fergus, who also wrote for "First Wave".
Split into simpler sentences: He is the son of the late playwright Michael Cook and playwright and actress Janis Spence. Sebastian has an older sister named Sarah, a younger sister named Perdita, and a younger brother named Fergus, who also wrote for "First Wave".