Well, the first thing we gotta do is get you a camera w/ a macro function; I can't really see anything in the pictures...
It's an interesting looking diorama. Which parts are resin and which are plastic, if any?
That pilot looks familiar. Revell's 1/32 Wildcat, or Corsair maybe?
If you want to take the paint off the aliens to repaint them, I'd use Castrol Super Clean. You should be able to find it at automotive stores. Use gloves, this stuff is unkind to bare skin. You should also be able to find some other advice for removing paint in the Techniques section of these forums.