There will always be a PNR for both the operating carrier and the marketing carrier. There will only be one PNR if (a) the operating carrier and marketing carrier are the same or (b) if they both use the same system.

QF and AY both use Amadeus so an AY code share on a QF metal flight will have a single PNR that both will recognise. Does your friends' itinerary include both an AY code share flight on QF metal and an AY flight (on AY metal)? I flew MEL-SIN-HEL-MAN earlier this week (in Y), with the flight to Singapore as the AY code share on the QF flight and the other two as straight AY; booking was made on the AY website. When booking, I could only select seats on the AY flights and not on the AY code share on QF. Tried to select seats on the QF website (OK) but doing so was clearly going to blow away the AY seats ("Seat selection not available - please select aisle or window") so had to bail out to avoid losing the AY seats. Called QF, who were useless. They couldn't assign a seat on their own flight, for reasons that weren't entirely clear, other than that it was an AY ticket. Called AY and after a long hold waiting for them to answer, got them to do the QF seats (bulkhead, both ways).

On a different topic, the QF service was stellar - purser came by to say hello, FA was very upbeat and kept coming by to see if I and the WP next to me needed anything, produced drinks from the J galley etc. - all-in-all a great flight (helped by starting off with a nice breakfast in the MEL F lounge). AY service to HEL and MAN was fine and had a couple of pleasant flights though some aspects of the AY product need attention, for example, no water handed out and no 'water runs' during a 12 hour flight - had to go get it yourself. The new QF lounge in SIN is pretty good - lots of space, didn't get crowded (I was there for 6+ hours) and a very large dining area (though the food was ok, rather than anything to write home about).