Complex sentence: Houston's solo performance was followed by ad-libs of its chorus part, later to be joined by BeBe Winans, Monica and Shirley Caesar who was seated in the audience and asked to do so by Houston.
Split into simpler sentences: Houston's solo performance was followed by ad-libs of its chorus. She was joined by BeBe Winans, Monica, and Shirley Caesar, who was seated in the audience and invited onstage by Houston.