You are posting really great questions!
I notice that you are certified by the American Council on Exercise. I found this information in ACE’s second edition of the Group Instructor Manual. Hope this is helpful to you!
Stretches, If Appropriate
“To stretch or not to stretch during the warm-up is a much-debated issue, and there is no consensus in the current scientific literature. ”
The text goes on to say that “instructors are in the best position to know their participants and determine what is best for them. The decision on how to go about warming up and stretching is an individual one. It is definitively known that flexibility is a health-related component of fitness and needs to be included in the workout. Whether it is at the end of the workout, in the middle or during the warm-up should be a choice made by the instructor based on feedback from the participants until more definitive research on the topic has been conducted. It is known that optimum flexibility is achieved at the end of the workout, and dynamic movement should be performed before any static stretching in the warm-up.”
ACE Group Fitness Instructor Manual, second edition pp. 177
Hope this is of help.