I agree with the folks that say there's not really a hole here. It's either a gang or its not, depending on what the MC decides. Gangs are mainly a shorthand that make it easier for the MC not to have to track the fictional positioning of a whole bunch of dudes all at once. If you've got some guys that aren't a gang, fine. Just track them individually.
And that means they act individually against the PCs too. Balls gets a clear shot off at you. Inflict harm. Tum-Tum lays down some covering fire to keep you pinned. Act under fire or maybe keep the fuck down, depending. Follow the fiction. Don't trade harm back and forth like its D&D.
And, remember, you don't Seize By Force against PEOPLE unless you declare that specifically, like "I want to capture Balls by force, mano-y-mano, it's him and me throwing down." Often times you're seizing some other kind of fictional objective. Like, "I'm going to run up that ridge, guns blazing, and take command of their machine gun nest." Still, that could be Act Under Fire too, perhaps, so it really depends on what else is happening in the fiction.
John Harper has a theory that Seize By Force is better thought of as an optional battle move, not something that gets used all the time, because it really means you're duking it out with somebody and that's pretty much a sure way to get killed in AW (since both sides take harm automatically when you use the move).
Hope that helps.