I completely understand the need for you to at least help your son narrow down some rental options. I'm not a realtor but I do work in real estate and I graduated Georgetown a few years ago, so I understand the housing options that students typically take very well. Most students live on campus -- has your son considered the many on campus apartment options, such as Village A (the upper floor units with rooftop access are very hot comodities) or LXR (I knew four guys with a 2 level LXR apartment with an exposed brick wall and a hot tub -- it was gorgeous)? How good of an apt he can get on campus will depend on his (or his roomates!) housing lottery pick (so encourage him to form a "roomate alliance" with some friends before the draw so they can all benefit from the best lottery pick of on campus housing).
When students do live off campus, it's almost always in one of the townhouses immediately surrounding campus (on Prospect St, N, O, or P Streets, etc.). Georgetown owns some of these townhomes, but private landlords own most of them. I've seen up to 9 students rent one townhouse, though, due to the high price. If he were to venture further out of Gtown, then Rosslyn and Dupont Circle are not bad options because the Georgetown University shuttle goes straight to campus from those two very metro accessible neighborhoods. And Georgetown does have a great housing office, so definitely talk to them if you're feeling like you need a clearer overview of all your options! Hope this helps :)