You do not have to always double up in the same register.
If you have six people on the stage other than the melody, you don’t have to put 2, 2, and 2 on the three main parts in the same octave. (You don’t NOT have to do it, either.) You can have someone double an octave lower from the melody or an octave lower from the soprano part. You can have one of the gentlemen sing the (usually unsung) bass part.
Just because the recording does it one way doesn’t mean you have to copy it exactly. In fact, you probably shouldn’t. You should always tailor what you do to the strengths of the team.
