Change Audio File(s) Tempo 72 bpm to 68 bpm AND Retain Proper Measures

Searched and read many audio tempo change threads and am quite confused. Here is my situation:

1.  The instruments are tracked at 72 bpm but the vocal doesn't work there. So I need to change the song tempo to 68 bpm to accommodate.
2.  Need to change the tempo and retain the pitch of 3 audio files:  bass, keyboard, drum (stereo track).
3.  And I want the 1st Chorus to still start at the 23rd measure, the bridge at the 57th measure, etc.

Guidance would be greatly appreciated.