There probably are things off the shelf (maybe look into car fleet trackers). This sounds like a fun project that you should just do because you can, though. Maybe later your charity can sell it to other organisations (paintball?) to raise some funds,
If you get the users to use their own phones, you will even get cell location enhancement and cell location when GPS is unavailable. Remember that mobile phones are trracking devices that make telephone calls
You could use RFID in addition to GPS. GPS is accurate to a few meters (10?) and RFID is cheap. They would be great for detecting when a room is occupied and by whom if the GPS cannot distinguish. I would even be tempted to make my own RFID senders with an arduino or similar, but it really depends on your time-scale. How long have you got? Whats the time constraints for this project?
I'll give your charity some licences for the Websocket API, gratis, if you want to stream the data via websockets to peoples browsers in their tablets or phones (you only need them for development). Webservices? Data Dashboard? Meh! I thought you wanted real-time That technology is sooooo 2000