I'd evaluate the train if you can get into the North shore line. You change at Wynyard for the airport line, it is fairly easy. You'll find lifts at the two stations and also the excursion from Wynyard is about 25 mins. Australia is on most travellers’ bucket lists, so https://sydney-domestic-airport-l51404.mybjjblog.com/sydney-airport-transfer-for-dummies-39825983