Sorry for separate posts, but trying to keep it organized.
Per 1028.2, the minimum width of the exit discharge would need to be the same as the required width of the exit, which for a total occupant load of 29 will be 36-inches.
The issue that may come up, is that the alleyway is going to serve as an egress court, therefore will be subject to 1028.4.2. In this case, the walls need to be 1-hr rated up to a height of 10-ft.
And here are the applicable definitions:
[BE] EGRESS COURT. A court or yard which provides access to a public way for one or more exits.
[BG] COURT. An open, uncovered space, unobstructed to the sky, bounded on three or more sides by exterior building walls or other enclosing devices.
[BG] YARD. An open space, other than a court, unobstructed from the ground to the sky, except where specifically provided by this code, on the lot on which a building is situated.