Can two different players play on the same computer?
At diffferent times, of course.
Yep, that's not a problem. You'll each need your own account here on the forums, and you'll need to download your own KML files. Once that's done, you're good to go.
Originally Posted by araf
You'll end up with two different GEMMO folders in Google Earth: "GEMMO - araf" and "GEMMO - whoever else". Just uncheck the folder of the player not playing, and then check the folder of the player that is. That should be it!