Years ago you needed 24 hour notice to get this "gate pass" as you had to be vetted for the no-fly list etc. ... presumably this process is faster now and maybe in real-time. AA would give a pass for Admiral Club access if you had meeting room booked at most airports, for example. Not sure if QF does this or not, it is a hassle for the staff and not all airlines at TBIT participate. Buying an Admiral Club day pass for $50 may be good value as it gets your parents access to the QF J lounge.