Complex sentence: Summers and Dennis left the group, forming The Gems with Mark Stevens and Alan Horowitz in 1960; while the remaining Brooktones signed to the Chancellor record label and added Jerry Serlen and William Shunkwiler to the group, while changing the name to The Dovells.
Split into simpler sentences: Summers and Dennis left the group, forming The Gems with Mark Stevens and Alan Horowitz in 1960. The remaining Brooktones signed to the Chancellor record label and added Jerry Serlen and William Shunkwiler to the group, while changing the band's name to The Dovells.