I think Vens heart is responding with Soras memories and the Keyblade, causing these weird dreams and creating multiple Soras, probebly because Ven and Sora created so many diffrent people, Xion, Roxas, Namine etc. Maybe they are all returning the part of them that they took but never managed to return after being absorbed. And when you think about it the Riku-Puppet was created from Riku which would explain him in the dream. And since Riku and Sora are both Keyblade Wielders they must be connected by the Keyblades, so they would enter this alter-reality together, am I going to fast? So I think at the start of the game they will enter analternative Twilight town, just for Keyblade Wielders, Ven, Aqua, Terra and Xehnaort (BbS) will also be there. Possibly the will be stuck there and need to do something to get out, but doing that will bring back all the evil Keyblade Masters back into the world, bringing about a new Group, the ORG successoers if you will, starting another adventure for Sora. So the Sad-Ones are the people connected to Sora who made all this happen. I'm guessing Kairi will be the one to stop it all, as she is a PoH, and possibly a Keyblade Wielder. The outfits are just memories, maybe you appear as you want in the alter-world?
But thats just my theory, sorry if its hard to understand.
