The one piece that puzzles me is how the frames are being captured from the iOS simulator. Are you launching multiples per user account, where each one is a different session at a different portion of the screen, and essentially screenshotting each? Or did you modify the simulator somehow and are hooking in to grab the screen, so that way its irrelevant of their position on screen?
We wrote some custom OS X code to capture frames from individual processes. That way the simulators don't need to be positioned in any way or even visible. Cheers.
The other piece of magic you are doing is sending in the keystrokes / mouse movements. If you're running multiple iOS simulators on a Mac, how are the key presses / mouse movements not interfering with other users?
Thanks!