It sure sounds like a 6 shot revolver would not have had enough ammo in this case.
A derringer would probably work, as the others will usually run away when they see one of their fellow thugs get his head blowed off.
I would think that dropping a couple of them accompanied by very loud bangs would obviate the need to drop all of them.
It would have. Shoot one and the rest would have scatted [ran]they are mean, not brave. Just as if you have a pocket knife in your hand when they are swarming you. Put the cold steel to one of them and he will move the rest.