There's also the possibility of NOT doing the song because of the lack of numbers. Never be afraid to say no to a song, no matter how much you like it.
We had to scratch quite a few songs because the singers just couldn't handle it.
There are alot of songs I want us to sing. But we can't because the 2 altos that we have; its hard for them to stay on their OWN key.
I deal with this problem also. I have one strong voice in each group (sop, alt, ten) on both the praise team and the choir and when one of them isn't there, I'm hurtin'.
When one of them sings lead, I usually have to switch them around so the rest can follow them and I'll hold down the tenor parts from the keyboard.
have one of the altos stretch themselves and sing soprano (if their voice can handle it).
Sometimes the ones that can't carry their own harmony can sometimes carry the melody if they know the song.
What you can try is let the alto who can't hold her own alto note sing the melody (or soprano).
Just work with what you got.