Hi Garth, you are right it can be confusing, I would suggest the following approach:
When your church is used as a church or any event where the public is gathered (including staff) you will need a fire management plan, does not have to be complicated just a simple management document that states the arrangements, roles & responsibilities.
The responsible person for the building has a duty to be able to successfully evacuate all "relevant persons" (any person who is within the premises), this can be managed by giving persons instructions for evacuation at the start of an assembly or may be that there are nominated persons (stewards, marshals) who would act accordingly directing/assisting persons in the event of an evacuation.
So if you had a church hall/service/meeting then you would have one or the other, however be clear that you must have a plan that will successfully evacuate the premises!
Just as a footnote if you hire a facility to third parties ensure that your hire agreement states that the hirer must understand that they are likely to also be deemed as a "responsible person" (& therefore must make necessary arrangements for evacuation) as they will also have control of the premises during their hire period/occupancy.