Yes - your parents should be able to get a visa at the airport upon arrival. I too suggest the meet and greet service. The name of this service is Al Maha and their desk is next to the rental car desks on the arrival side of the airport. We used it for my husbands parents and you can pay for their visas up front and Al Maha will arrange the visas for your guests as well as escorting them through immigration and baggage claim. Also, they walk your guests out to the arrival waiting area and stay with them until you come forward to pick them up. My husbands parents thought it was great.