Browsing through the UGO HeroMachine forums, I've seen a number of "group shots", characters all built around a common theme and then assembled together in Photoshop. But I think this trio from "Count Libido" (don't let the name scare you, it's all clean), called "Linkin Green":
All of the Count's character images are really well done, even stretching back to 2005 (!) and the earlier HM versions. Note in this Linkin Green group how well the color palettes match. They're obviously three individuals, but just as clearly they're part of a group, and it's done by setting a simple four color palette and sticking with it. A common mistake when making characters is to load every color in the rainbow onto their outfits, but that just looks like a peacock exploded on them. Keep it to a tight group of colors like Count Libido and you'll end up with a much better design.