Don, Without roadies and a sound engineer you must rely on band members themselves to balance the sound as they play. You can set the mic levels before the gig so that each instrument could achieve the maximum desired volume but below the feedback level. That's about as much as you can do with mic levels. What you really nead is monitors. These can be monitor speakers or the modern wireless earpieces they're using today. This will allow each musician to hear his or her own level with respect to the group. As long as you have general agreement on the desired agrigate sound, you'll be fine. Players who are too soft can lean into the mic while other can move away if needed. If you're using electric instruments and micing amps they'll need to adjust their instrument controls as they go.

Early bluegrass bands used to record and perform around a single omnidirectional microphone. They developed an elaborate correography around the mic to balance the sound and bring the lead instruments up for their solos.

Good luck,

      - Mark