Change C of O and Sprinklers

We are currently in contract on a detached house with a 1956 C of O for three units (one on each floor). The house has been set up as a single family for a long time, but there are no records of permits being filed by previous owners for any of the alterations that must have occurred. There are no violations, either. We have a few scenarios in mind for this house, but we have received a lot of conflicting information about what kind of alteration permit would make the most sense for us. In one scenario, we add back in two kitchens and restore the home to three units. The upside to this is income, the (major) downside is each unit is relatively small – the unit we would live in would be smaller than our current apartment, which wasn’t really our goal in buying a house. In another scenario we create an owner’s duplex and an attic rental, but in order to do this and have private access to the upper floor of the duplex, we would need to add a staircase.

We have been told that in order to be approved to build a second stair, we will have to change the c of o to a two family. I know conventional wisdom is it’s a bad idea to reduce the number of legal units, but in our case we don’t think it would significantly reduce the value of our home based on it’s set up and location, and it would allow us to create the duplex we want as well as possibly use air bnb as another source of income (air bnb being no bueno in a 3 family). Does anyone have experience that can confirm that we would or wouldn’t need to change the c of o in order to change the configuration of the home to a two family?

Another major concern is avoiding the expense of sprinklers. I have read through a ton of posts and waded through the building code, but we have literally been told opposite information by two different professionals, so interested in what the collective here thinks. One expediter says if we do anything to change the occupancy, that would trigger the requirement to outfit sprinklers. Another expert we consulted said to restore the three family would require sprinklers, as the number of units would increase from the current configuration, whereas reducing the c of o would avoid that requirement because sprinklers are not required in two family detached homes. FWIW, there is an existing fire escape, providing two forms of egress from each floor. Anyone have thoughts on who is correct?