If you are a member of a club and have insurance through that club (typically included in your membership fee) you are covered for all legal shooting activities including instruction. If you are teaching people with no membership and therefore possibly no insurance, then you need to make sure you collect money from them that goes to the club to cover guest insurance and have them sign in. If you do that, then all are covered. Instructors are free to carry extra insurance which can also include covering their students, but in BC at least, and I would suspect the rest of Canada it's not necessary.
As well, police officers who are shooting duty weapons either for practice or at quals are covered under their municipal or federal insurance programs and do not need insurance from a club to shoot. I know of a few clubs that prohibit LEO from using the range with duty guns and gear on their own time as they think they aren't covered. They are, it's Fudd boards that are anti cop that come with these stupid rules. Their insurance is government bases and is far better than anything we can buy as club members.
edited to add this for the insurance BCWF provides clubs in BC, I believe if I recall the conversation correctly, that the NFA provided insurance is the same.