In the scene where Eddie Murphy is going into the crypt, he takes one of the lit torches. While they are trying to escape the skeletons, the door to the crypt closes and locks. When they show the shot of his son outside, you see two torches again. When he gets the doors open and they leave, you see one.
The voices for the singing busts are provided by the Dapper Dans, a barbershop quartet that performs regularly at Disneyland park in Anaheim, California.