If you want the meet and greet service at the airport it needs to be organised beforehand. I suggest your friends go to the Qatar Airways office and book it. They can pay for everything in advance and you need not worry about anything when you arrive. Like I say, you can even get your luggage picked up. For the moment I have forgotten the name, I think it's Maharaba Services. There is also a counter at the airport, but thats too chaotic to visit at the moment and would avoid, Qatar Airways office is best, I used the one at City Centre Shopping Centre.
Just to let you know, my friends sister arrived last night from UK and had no problems at all. Was not asked to produce anything.
Good Luck.