Barb,
I don't think the fact that this photo was taken in Australia is significant in you not receiving any replies. You only posted the photo a couple of days ago - sometimes you need to wait a while for an expert to come along.
May I suggest that you try to obtain a better scanof this photo. It is small and blurry when I try to zoom in to look at the detail. I think this is may be deterring people.
Contrary to popular belief, the fashions and dates would be similar worldwide. As to why the women are wearing the same outfits, we can only speculate. The men's buttonholes are likely to be significant. A clearer scan might reveal more detail and clues.
A quick glance makes me think this might be early 1900s.
Have you tried google? The studio still exists:
http://www.whiteheadstudios.com.au/whitehead-collection/people-weddings-portraits(They were established in 1883 by FA Whitehead, so your photo will be later than that.

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