AA will not
tag bags through on separate PNRs/tickets, even when it's oneworld airlines. There may be some specific exclusions to this, but basically that's how it works for your scenario.
In any case, it's entirely irrelevant if they will
tag the bags through to BNE or not, given that regardless of how your flights are ticketed, you must collect them in Sydney, and you must drop them off at the Qantas domestic transfer drop off area, which is a short walk from the international arrivals.
If your bags
were tagged through to Brisbane, you would drop off the bag at the drop off counter at the domestic transfer.
If your bags
were not tagged through to Brisbane, you would still go to the domestic transfer area, but line up to check in and get your bags tagged to BNE.
In both scenarios, Qantas takes your bags from you at the domestic transfer desk, and you proceed through security there at the transfer, and ride the transfer bus airside to the domestic terminal. Then you go to the lounge, or go to your gate and fly back to Brisvegas.
From the Qantas website on transfers from Sydney international to Qantas and QantasLink (not Jetstar) flights:
Sydney T1 international airport guide | Qantas
Transferring from T1 (international airport) to T2 and T3 (domestic airports)
The transfer lounge is located on the arrivals level of Sydney International Airport. After you clear customs, follow the signs located outside the terminal; entry is outside of the main terminal within a short walk via a weather protected walkway. Recheck your baggage at the seamless transfer check-in counters and then board the shuttle bus for the domestic terminal. It operates from:
- 6 am to 12 pm every 10 minutes
- 12 pm to 9 pm every 20 minutes.
The bus arrives at T3 at Gate 15. Check the screens for departure gate information.
Passengers connecting to a flight not operated by Qantas or QantasLink should refer to the Sydney airport website for further information on transfer options.