Our trainings also vary by the delivery. It can be a solo training delivered by one trainer, or it can be delivered by duo when two trainers are present along the course, or there is a variant when the secondary (visiting) trainer joins the course for one or a half day. And also we do slicing when trainers change each-other among the days.
The general rule that a single trainer can work with a group up to 16 attendees, and when the audience exceeds that size it's preferable that a visiting trainer joins the course delivery.
Over 21 attendees a duo should deliver the course. Over 30 attendees assisting trainers join the delivery team to help the attendees with the exercises.
With adding more trainers to the course delivery the price raises accordingly.