I find it hard to believe that you know of a family who came to HK from Australia and they were not offered a place in AISHK. They have a policy of always accepting the children of people who come to HK mid term.
If you are Australian you do not need to pay a levy, just the $10,000 January ripoff. I have never heard of them not accepting an Australian child who applied at the "right time".
As for ESF, there is a shortage that the HK government wont publicly acknowledge (must not provide whitey, i mean English, education in the glorious workers paradise).