Brenda, Brenda Performance

In the part where the staff put on thier performance (Brenda, Brenda), the miming of Jasmin and Brenda is absolutely terrible! Especially on Jasmin, only about a quarter of the words are believable. Do you think they were meant to be singing, or miming, or was it left for the viewer to decide, made to think because of the bad miming?
Many thanks,
Louis