Are you sure QF fly this route? From the few dates i've looked at, there is a Qantas codeshare with Fiji Airways, but not actually Qantas metal. The same is true of SYD-NAN.

Jetstar operate NAN-SYD, and they are part of the QF family (wholly owned subsidiary), but are not One World, ergo not a BA partner.

A quick check of the NAN Wikipedia page (which of course isn't always correct) doesn't show Qantas as an operating airline.

https://en.wikipedia.org/wiki/Nadi_I...d_destinations