Heath Ledger provides the model for the Joker, but Harley Quinn is rendered simply from her comic book design since she was never featured in any of Nolan's Dark Knight films.
An image showing a method for attaching Harley's Heads is below. Also, an image to suggest at least one way of coloring the characters is included as well. In the comic books currently, both characters have white bleached skin (as opposed to the makeup The Joker used in the film). Also, Harley's hair was originally blonde, but depending on what depiction you are looking at these days, she wears it dyed a variety of colors/styles.
I've also included a sequence from Batman: Legends of the Dark Knight (no. 142) in which the Joker decides to take a bath in Ra's al Ghul's Lazarus pit, which is where I got the idea for the doll's underwear. The only thing I changed was that they are sad faces in the comic book. I didn't realize that when I drew mine. May have to go back and fix it.
The Joker was created by Bob Kane & Bill Finger and is the property of Warner Brothers / DC Comics. Harley Quinn was created by Paul Dini & Bruce Timm and is the property of DC Comics. These dolls are intended for your personal amusement and should not be sold for profit or broadly distributed.
Here we have Christian Bale as Bruce Wayne / Batman, and Joseph Gordon-Levitt as the Robin of your choosing ~ he could be Robin John Blake, Dick Grayson, Jason Todd, or Tim Drake.
For obvious reasons he can't be Stephanie Brown or Carrie Kelley (two female Robins who are no longer part of regular comic book continuity). He probably won't make a good Damian Wayne either (too old). At least the other Robins all reached a relative age of maturity at this point, though they have also left the "Robin" persona behind to become, respectively, Nightwing, Red Hood, and Red Robin.
Joseph Gordon-Levitt's John Blake was played as a much darker, straight-laced character in Nolan's Dark Knight Trilogy, but I've given him a smile here as Robin is typically more light-hearted (to balance out Batman) in the original comic and most other media.
Batman & Robin were created by Bob Kane and Bill Finger and are the property of Warner Brothers / DC Comics. These dolls are intended for your personal amusement and should not be sold for profit or broadly distributed.