Well it's a flashback scene, third person past tense, e.g. "Bob picked up the glass of milk and drank it." The observing narrative enters into the scene when everyone is gathered. It's a train car, so I suppose I could have at least one or two person(s) entering from another carriage, but it wouldn't make sense if everyone was spread out throughout the train.
And like I said, there's quite a few characters with very strange features that would warrant immediate attention, since it's also close to the first time the protagonist is introduced to them (right before they got onto the train) as well as when the narrative first includes them.
I plan to show a bit about their personalities through how they interact with eachother, since they are already acquainted between themselves, but as for the visual cues... I don't want it to drone on, but I have a lot of information I want/need/feel inclined to dish out about each individual case.