Complex sentence: In the early 1960s, at the age of 13, he was half of a singing duo with his twin sister, "Elaine and Derek" which released one, eponymously titled album on the Parlophone label.
Split into simpler sentences: In the early 1960s, at the age of 13, he was half of a singing duo with his twin sister, "Elaine and Derek". They released one, eponymously titled, album on the Parlophone label.