Complex sentence: Billy replaced former singer Steve Souza in 1986, prior to the recording of their first studio album, "The Legacy", and has been a member of the band since; he and Peterson are the only band members to appear on every album.
Split into simpler sentences: Billy replaced former singer Steve Souza in 1986, prior to the recording of their first studio album, "The Legacy", and has been a member of the band since. Billy and Peterson are the only band members to appear on every album.