Anyone in city of Buffalo NY have experience converting a 2-unit building to a legal 3 unit?

[Julie Greene]

Long story short, we had been looking to purchase a 3 family unit that is currently only on the books as a two unit.  The contract that we received specified that it was a three unit, so seller would need to provide legal certificate for a 3 unit.  Seller does not actually want to deal with converting it as he no longer lives in town, and because he bought it three years ago when it was listed as two unit and had no problems renting the three units.  So his lawyer disapproved the contract .  We are still interested in the property, however, we are extremely wary of operating as a 3 unit building if it's not zoned that way.  At the price we had agreed on, the place is not worth it as a two unit.  I had a quick conversation with an architect who did an initial walk through of this property a few months ago, as the owner was considering converting it.  The architect hasn't actually done any work on this project beyond walking through it - I asked him what is usually entailed in a conversion from two family to three family and he mentioned sprinklers.  Does anyone else here have any experience with this?!? It is a 100 year old brick structure that has one unit on the first floor, one unit on the 2nd floor, and a third unit that has a bit of space in the basement and first floor.  I clearly have a lot to learn, but I am currently frustrated...I don't know how to determine whether the property can even be converted legally, and how much it will cost (since I don't yet own the property).  Can anyone point me in the right direction?  I feel like  I am getting in my own way here and I'm kind of paralyzed...if I need to walk away I am ok with that, but I'm not sure how I go about determining this!!

Any help/guidance is appreciated!