Complex sentence: McNamee on vocals, guitars and keyboards; and Williams (who, at the time, was also a member of Philadelphia Grand Jury) on drums and vocals the band were booked to play gigs before they had created any songs.
Split into simpler sentences: McNamee on vocals, guitars and keyboards; and Williams (who, at the time, was also a member of Philadelphia Grand Jury) on drums and vocals. The band were booked to play gigs before they had created any songs.