Senna incident is a good example of what can happen with more than 2 cars side by side. Both Senna and Vettel are concentrating on the car between them. Vettel doesn't allow for another car passing on the inside, and Senna isn't trying to pass Vettel, which is why it ends with a front wheel to rear wheel collision. Technically not sufficient overlap for a pass, but Senna is just trying not to hit him at that point.
I hope Vettel thanks whoever built those suspension arms, because those two hits both looked harder than the one which broke Hamilton's car. Maybe they weren't, but still, so lucky to get away with it so lightly.