AA rules are currently unlimited travel within the mileage level and award amount as long as...

-you don't stopover or connect through your point of origination
-do not stopover in a city more than once
-do not connect through a city more than twice

So you could stop once in SYD in excess of 24 hours and then connect through SYD twice as long as each time is less than 24 hours.

If other than AA, you have to use two additional Oneworld carriers so you could use only BA, but if using AA, then you would have to use two additional OW carriers.