Complex sentence: His eldest sister Carol was followed by triplet brothers, Jeffrey, Leslie and Stephen, and then by Corky, whose brothers called him "Gorky" because they could not pronounce his given name.
Split into simpler sentences: His eldest sister Carol was followed by triplet brothers, Jeffrey, Leslie and Stephen, and then by Corky. According to Corky his brothers called him "Gorky" because they could not pronounce his given name.