Do the old houses fall under the code? 101.2 applies to all buildings including "alteration and movement" but Exception 1 exempts multiple single family dwellings (townhouses) less than 3 story.
Section 310 classifies various living qualities into R-1, R-2, R-3, and R-4, but "townhouse" is not included. The definition for dormitory adds "as in fraternity houses". It would seem that the function would tend to classify the houses as "dormitory" and therefore Occupancy R-2, unless excluded by 101.2, Exception 1.
One of the problems in working with plans for the two houses involves stairways. Residences, especially old houses, have stair configurations that are far from current codes. I have a certain area where the old basement stair was located in which to construct the new stair into the new basement. If I use legal rise and run dimensions, I'll have to cut into adjacent spaces to provide legal rise, run, and headroom. Section 3403.4 says "replacement of an existing stairway in an existing structure shall not be required to comply". I find great relief in that paragraph.
On the other hand, Section 3408.1 states "structures moved into or within the jurisdiction shall comply with the provisions of this code for new structures". Ouch. There are undoubtedly deficiencies in door width, wall construction, fire ratings in these 40- 60 year old houses when compared to new code requirements.
If I attempt to classify as Type VB, 0hr ratings, I see on Table 602 that the two walls that are 15'-7" apart should be one hour rated (now wood framed with siding). Does this requirement go away when the two residential wings are joined by the future activities center?
I'm fairly certain that corridor wall ratings, HVAC, and electrical are far below code. If exempt by 101.2 as a multiple family dwelling, then it goes to the IRC. If pinned by 3408.1 there will be a lot of remodeling before this job is done.