Split them into a preshow team and a postshow team, one set handles sweep and mop before the show and the other set handles cleanup? Or split this between performances? Depends on how many performances you're doing, though-- if it's only one weekend, that might still leave too many.
You should talk to the proff and let him know you've got too many, otherwise it's just going to lead to a backstage full of people sitting around doing nothing, and, worse, chit-chatting out of boredom.