Are these plumbing vents that have been capped? I am not sure what these are. This is on a 1920 era home.
Any access to the roof space? Any vent stacks anywhere else? Where is the kitchen/bathroom/laundry installed? No DWV coming out of the side of the house? They could be DWV but maybe they are not used anymore due to renovations over the years? Any problems with the drains in the house? I would confirm operational vents and relate them to the fixtures below the structure. If they dont make sense or there is doubt recommend FI by a plumber.
If you can pull the caps and run the fixtures in the building you can usually hear the water flow…
After further inspection this appears to be from old DWV that are no longer used. This is an old home with much of the original electrical and plumbing in place which the buyers are going to completely replace.