There are also double triple-deckers (six units)- the stairs are shared by two triple-deckers sharing a common wall. Most of these are side by side, but in Worcester, there are also front / back ones like this (134 Elm St.):
https://www.google.com/maps/@42.2661816,-71.8159232,3a,75y,1...
or with turrets:
https://www.google.com/maps/@42.2662587,-71.8167573,3a,75y,2...
The stairs are definitely shared in the side-by-side ones, not sure how it works in these.
So I used to rent in a 10-unit five story brick and wood building with front and back stairs, so I question a bit that the two stair requirement is such a big deal. This building had a central open area, and an old (broken) cage style elevator. Something like this:
https://www.google.com/maps/place/Taboo+Beauty+Salon/@42.264...