Complex sentence: The idea was gestated in Paul McCartney, who composed many of the songs in the suite, in addition, John Lennon, George Harrison and Ringo Starr each contributed songs, or parts of songs to fill in the empty bars.
Split into simpler sentences: The idea was gestated in Paul McCartney, who composed many of the songs in the suite. In addition, John Lennon also contributed songs, or parts of songs to fill in the empty bars.