As we observe, Ming is not taking lip from any of them, wanting them to submit to her. It sounds rough as she tries to tell them who is boss. Occasionally we hear some loud growling but we were assured by old Westie hands that this is entirely normal. Some of it is playing, other disciplining, and teaching.
Below is a video of Ming and Pink. Pink is staying as a permanent member of our household and she gets the most "attention" from Ming of the two pups primarily because she challenges Ming more. She may have a stubborn streak as well. Ming usually just runs around and plays with Duncan while disciplining him occasionally.