At Epcot, you go in one entrance. In September, the characters were Mickey, Goofy and Minnie, but each one had their own spot for photos. You do one character, then move onto the next one, then move onto the last one. It is not a photo with multiple characters. PP covered Magic Kingdom and DHS.
If you have a Disney Visa card, one of the perks usually is a photo with characters, but they never tell you which characters in advance. If you have the card, you can post shortly before your trip to ask which characters it has been lately. You probably would want to ask that question in the Theme Park Attractions & Strategies forum; it gets more traffic than this forum.