Complex sentence: They formed a music duo they were eight, naming it "Hubba Bubba" after their favourite bubble gum, and also starred together in professional musical productions such as "Annie" and "The Sound of Music".
Split into simpler sentences: They formed a music duo they were eight, naming it "Hubba Bubba" after their favourite bubble gum. They also starred together in professional musical productions such as "Annie" and "The Sound of Music".