Need of sprinkler after renovation? Going from 5-family CO to 2-family CO

This is a question I would have thought would have been very straightforward, but I can’t seem to get a single answer.

House built in 1845. Certificate of Occupancy from 1966 as a 5 family. City taxes as a 4-6 family. Deed has it listed as a 4 family. We want to renovate and bring it to a 2-family – garden floor apartment + upper floors unit.

Most architects I speak to say something to the effect of “That is an alt-1 so you will be forced to put in a sprinkler.” A contractor I have worked with in the past though doesn’t see why we would need a sprinkler put in, and said in his conversation with an architect “Generally speaking, a two family should not need a sprinkler system. Two family usually falls under the same life safety rules as one family (assuming each unit has separate and adequate egress).”

If anyone is an authoritative pro and can provide some informed insight, or could recommend someone for me to speak to, that would be appreciated!