Try to find the spot where the photographer was standing.
The imposing gatehouse: srnsw: [https://www.flickr.com/photos/state-records-nsw/8344226284/in/photolist-dHmkLq-9yC2CF-dUW6Y1-dUW6VC-pADjoT-aGUxpX-oeQ84s-oePXiM-ow3AwX-dUQwjP-i8LT3Q-hU5WV6-hRf1ax-dUW6Wh-dR7UTS-dRXFm6-ouhN8m-ouhMY3-aBDCDp-oeQ5mU-oeQ3P6-owjN1k-owjGLH-owjGZZ-oeQPpr-ow7Fwb-ow3C4V-ow7BhE-oeQMtH-oePQ6S-ouhRGL-owhWz5-oy5vtg-oy5wR6-ow3D1K-ow7F5u-bd5wzT-aGUKh6-aBDANe-aBDA5V-aBDACv-aGUymT-ouu6bh-dtz2hS-dttu7i-dtz2jo-dtz2eo-dttu2c-owdTPq-ow6y6D]
Thanks State Records for the huge size. That has to be the NSW Governor, Admiral Sir Harry Holdsworth Rawson, GCB, GCMG (1843 – 1910)(NSW Governor 1902-09), his wife Florence Alice Stewart, and a daughter. en.wikipedia.org/wiki/Harry_Rawson - see illustrations. Also adb.anu.edu.au/biography/rawson-sir-harry-holdsworth-8162
Those were the days Photo ! ☺
From the wikipedia and adb articles (linked above) - Florence, the wife, 'a kind gentle-voiced motherly grey-haired woman' died at sea in 1905, and daughter Alice took over her mother's duties. I wonder if this is Alice in the photo? The Alice Rawson School for Mothers was named after her -
So, the photo is between 1902 and 1905.
See 'Vanity Fair' portrait, Men of the Day, No.807 by 'SPY' in 1901