I’ve already done an MBSR/MBCT/MSC 8-week course, do I still need to do a Breathworks course as a prerequisite for teacher training?

Yes. Although there is some overlap between the contents of Breathworks courses, and other 8-week mindfulness courses, there is enough that is distinct about the Breathworks approach that will make having participated on a course yourself indispensable to training as a facilitator or teacher in the Breathworks approach to mindfulness and compassion. You can complete either a Mindfulness for Health or a Mindfulness for Stress course to fulfil this prerequisite.