Complex sentence: Jardine fully rejoined the Beach Boys in the summer of 1963 at Brian Wilson's request and worked alongside Marks with the band until October 1963, when Marks quit the Beach Boys after an altercation with the band's manager, Murry Wilson.
Split into simpler sentences: Jardine fully rejoined the Beach Boys in the summer of 1963 at the request of Wilson. Al worked alongside Marks with the band until October 1963, when Marks quit the Beach Boys after an altercation with the band's manager, Murry Wilson.