Lastly, I have lived in 2 different large houses converted to apartments - once when I was a child, and once a few years ago when DH and I were just starting out. Neither of them had finished basements... but both did have access from outside the house. One via cellar... The other just a small flight of stairs going down, as thats where the washers/dryers were. I have to say, though, that if there is a finished basement where somebody actually sleeps, I don't think there would be access from outdoors. If somebody were to go through the trouble to turn the house into several apartments and include the basement, they would probably also go through the trouble to wall off any outdoor access down there. Seems like if anything ever went wrong (things stolen, or the apartment easily broken into, etc) it could be big trouble for the property owner. So I just don't think there would be any way into the basement except for inside the house itself. And any windows would probably be the small sort. If anything, I would hope that IF there were basement access from outdoors, the parents would take that as their bedroom and keep the kids where its less "open". I would...
It does look like there might be basement access from outside in those pictures, and of course I have no way of knowing, but I truly think it is probably blocked off/walled in/drywalled over, etc.
All of the above... JMO