"In instances such as this, where innocent victims are attacked, we will work tirelessly to hold those responsible to account."
Cottam said the actions of the "quick-thinking member of the public" who rang police, was a great example of the public and police working together to keep communities safe.
The two victims received a hospital check-up after the assault.
They were shaken but not seriously injured, and police are continuing to offer them support, Cottam said.
A 39-year-old woman had been charged with aggravated robbery and two charges of aggravated assault. A 38-year-old woman had been charged with aggravated robbery.