Complex sentence: In the early 1970s they lived together in a commune on the Isle of Anglesey in Wales, where they performed their own musical compositions with Paul Mattocks, who played flute, guitar and keyboards.
Split into simpler sentences: In the early 1970s they lived together in a commune on the Isle of Anglesey in Wales, where they began to make their own music. Among the many would-be musicians was Paul Mattocks, who played flute, guitar and keyboards.