You have immense potential for getting people mad at you here.

Especially if there are two acts performing, one a solo or duo and the other a group of several people. Splitting the take evenly between the two groups unduly favors the performers in the small group. Splitting so as to produce the same sum for each person unduly favors the large group, since the performers in the small group are presumably entertaining the crowd just as much as the large one.

And you haven't mentioned the question of whether one of the groups may be better known and draw more people than the other.

Whatever you do, make sure both groups are fully informed as to the arrangement, and agree to it, before the gig. Get it written down and signed.

Peter.