public transport to Orly from Paris for 4 people will cost about 48 Euro; it is 30 or 35 by cab. It was never economical to use public transport from Orly with more than 2 people. And it is not much better from CDG; 40 Euros to carry your bags up and down stairs, be vulnerable to pickpockets while you are carrying all your valuables, and then walk to your lodging versus 50 or 55 for door to door service by cab. As others have noted the metro does not go to the airports; it covers Paris only and the airports are well outside Paris. But the suburban train ticket you need from CDG allows transfers to whatever metro you need to get to your destination in Paris. But get a cab.
Versailles costs about 7 round trip (you buy two tickets -- to and from for each person) A carnet of 10 tickets for transport within Paris is 14.10. With your schedule you only need metro tickets for one day; one carnet will do it for the group if you plan that day carefully with much of it walking.