The Soprano part is as written and as sung on the audio parts.
Alto’s are to sing the written Alto line until the B section (bar 13) at which point the part splits, here all Alto’s should sing the Alto two line.
Tenors are to sing the written tenor line until the B section (bar 13) at which point the part splits, here all Tenors should sing the Tenor two line.
Unfortunately, there is no written Bass part. As such, Basses are to sing along with the Tenors in the verses, splitting to the Tenor one line in the B section. In the choruses the Basses should sing the octave down from the Soprano part.