Couple of points here; first, merely bringing a gun into the picture may not be enough by itself to stop the act. But adding a formidable command presence will go miles over someone brandishing that does not sound like they mean business.
As far as the 2 adults stopping the action, someone stated it was never indicated whether or not they were armed. In this scenario, I think it proves that a determined action trumped the toads higher numbers. If they were armed, the 24 or so obviously didn't want to tangle with them, even though they outnumbered them 12 to 1. If they were not armed, it proves it even more.
I don't think any of the posters advocating action here are taking on a "Rambo" persona by doing so. Mind set, training, and command presence work on larger groups; it has for me, and that never involved rushing headlong into the fray.
And if the thinkable happens (I don't like the term unthinkable, as it implies one cannot keep their head and tactically act), looking at the interior pic on the train, you could pick a choke point to limit the toads ability to use numbers to their advantage, such as just a step this side of the 2 upright poles next to the seated guy on the left. Not a great funnel, I admit, but start filling it with thugs, and it becomes harder to press an attack.
Lastly, this is not a riot by hardened lifer's that will operate as a mob. This is a largely a pack of cowards, led by a couple of stronger willed cowards. I agree, if deadly force is called for and you drop the leaders, the rest of the pack will do whatever you tell them to do to stay alive. My .02.
Busting thugs since 1992