Complex sentence: Holt became the band's singer, and they would bring onboard keyboardist Rick Wakeman who proved unreliable, and when the first demo was recorded in April 1970, the latter was replaced by Frank Wilson.
Split into simpler sentences: Holt became the band's singer, and they recruited keyboardist Rick Wakeman who proved unreliable. When their first demo was recorded in April 1970, Wakeman was replaced by Frank Wilson.