Besides the accordion?
You've got 12 mic channels on your 1602 - are both bands playing at once? If not, set up your board to be ready for both bands. Tell the keyboard players that mono will sound great and everyone in the audience will hear everything. Set up your mixer to be ready for both bands something like this:
1-4 drums (kick, snare, 2 condensers - hat OH or 2xOH)
6-7 keyboards (can be the first bands keyboards and then the Arranger and solo keyboard)
8 Violin Mic
9-11 Vocal Mics
this leaves you with one extra mic channel if need be for the drums, or if a bass player stumbles in. So you know, our band for indoor gigs does the 4 mic on a 5 tom drum kit and it sounds fine - you don't always need to mic every drum.
Only thing you have to repatch during the show would be the keyboards. Mute the unused channels in each show, and bring one less piece of gear to have to worry about.
 I wrote my post right after Dick's and before seeing the bands must go on right after each other. [/edit]