I'd suggest using booking.com to search for a hotel. A "family room" will be the cheapest option for three people, but they may need two rooms instead. Look for a place near a Metro station, preferably where two lines cross. I'd suggest the 5th arrondissement (Latin Quarter) where there will be lots of students, or the 13th just to the south. You can filter by location, price range, and other variables. Pick a few candidates and then use the hotels' own websites to contact them directly for a reservation. You can the "street view" feature on Google Earth to eyeball the hotels and neighborhoods, and connect to their websites.
Better still, have your son and/or his friends do this search. They'll need this kind of travel skill in the next semester and beyond, might as well start now.
An ordinary taxi, whoever is first in the official line at the airport, should be just as good as Uber. There are cheaper ways to get into the city but for three people with luggage, who haven't used the transit system, a taxi would make more sense. But after a couple of days in the city they might be able to take the RER commuter rail back to Orly for the departing flight. The "B4" train stops at Antony, where there's a connecting "Orlyval" line straight to the airport.
Looks like all this is happening next week, so best to get going fast. January's not the height of tourist season, but places will still be filling up if not full already. Hope they have a wonderful experience in Europe.
