I'm trying to get my head around this.
I'm flying Asiana, LAX-ICN-MNL for my brother's graduation in Manila. The return is MNL-ICN-LAX. At the end of the trip he will be coming to the US. My ticket is ~$1000 but if I book his ticket on the same MNL-ICN-LAX itinerary, his ticket is ~$2200.
I can book a ticket on Philippine Airlines MNL-LAX for $700 from the US but then we wouldn't be on the same flight.
I called Asiana airlines and they said that I would have to book through a travel agent in Manila to try and get a lower fare. I also couldn't pay with a US issued credit card for the roundtrip LAX-MNL flight.