It's simple to use two characters of the same type. This video shows you how.
Adding two Callies to your scene is as easy as hitting the Add Element button, choosing Callie, setting her mark, and repeating the process. By default, both characters will be named "Callie" in your track list. You can select the specific Callie you want by tapping her in the camera view (withTo your mouse on a laptop/desktop or using touch on a tablet), or you can rename one of the Callies to help you keep track of which is which.
To rename an element, select the element and then hit the "Gear" button to access the element's properties. Tapping on the name property allows you to change the name. After changing the name, hit return and use the "Back" button to close the properties viewer.