I highly recommend the Miramontes family and use them often, however when it comes to people arriving at the airport I strongly urge you to have your family hire a taxi there. It's so easy that I don't even pick up people anymore and here's why: as mentioned earlier, any kind of delay with their flight will have them stressed that you're sitting around the airport waiting for who-knows-how-long. Travelers don't need more stress. Any protests or construction blockages are hard for private taxis to get through sometimes and the airport taxis have priority and know the ropes. Don't forget traffic delays on the highway if there's an accident that hasn't been cleared; now everybody's stressed.
There is a clearly marked taxi kiosk just inside the airport as passengers come out from customs. The price is fixed, tell them how many personas and show them the luggage. You pay at the kiosk and they hand you a receipt. You walk outside, a man will see your receipt and find the right size taxi for you.
Easy as 1-2-3 and no one gets stressed.