Edit an animated gif

Design details: I have an existing animated gif that needs 2 areas of editing:
1) add additional characters to a 70 frame gif (currently 4 people in a car, need it to be 6)
2) replace faces of new 6 people with new still images
Ideas for the visual style: Attached gif to indicate direction
Extra notes: Attached is a very similar version of what I am trying to create. The additional requirement would be to add an additional 2 people in the car.