With this route you need to be very very flexible.
Iv managed to get the dates i wanted for honeymoon, 1xY sector, 2xCW and 1xF, fingers crossed that F opens up to change the Y sector but im sure something will crop up nearer the time !
Check daily, or even more, then grab what you can and when you can, your biggest problem is going to be bagging 4 seats which i have never seen on the BA routes, however if your not using a BA 241 voucher your options are much vaster !
Currently you can mess around with availability and routes between BA, QF, JL and CX.
There is also the option to make it a bit of a longer trip, LHR-LAX-HNL-SYD etc (BA, AA, QF)
Best tips are be flexible and also break the trip down into sectors and search each sector on ba.com rather than trying to get the website to plan your trip as a multi city routing
cs