The only way to stop a bad guy with two guns is a good guy with two guns. Two good guys with one gun apiece would probably work as well.
The only way to stop a bad guy with three guns is a good guy with three guns, or three good guys with one gun apiece.
However, two good guys — one with two guns, the other with a single gun — wouldn’t work. You don’t want the good guys spending all their time fighting over who gets the second gun.
And don’t try to argue that good guys don’t fight with each other over petty stuff. Did you miss Captain America: Civil War? That’s all good guys do is fight each other these days.
In order to stop a bad guy with three guns, two good guys with an unequal number of guns might work together if you sent them to a teamwork seminar or something. You’d have to weigh the cost of hiring a third good guy versus the the cost of the seminar. Just don’t go cheap and sit them in front of computers to watch a webinar together. In-person training is the way to go.
Don’t worry about bad guys with four guns or more, because how would a bad guy shoot them all at once? They’d need four arms. I suppose the same could apply to a bad guy with three guns, although some bad guys might have three arms. That sounds like something bad guys would have — an extra arm. But four? We’re talking about people here, not insects.
If you run into an insect big enough to hold a gun, you’re probably living in a world where people have superpowers. In that case, just let Superman deal with all the bad guys with guns. Problem solved.