How about this..
We make it so you need at least 5 members in the room to do gang spar, for both gangs. Each member of the winning gang gets a gang point?
OR
We could make it so, again, 5 members are required. But before the spar starts, the gang has to bet gang points. Maybe each member would be required to put 1 in. And then the winning gang members get the points? And maybe you could have the option to bet 2 or 3 too.
Ideas?