Do you mean that Giuseppa and Giuseppi Vassallo emigrated to Australia or Giuseppi's parents emigrated to Australia? Do you have any other information on the Vassallo family or their offspring.
As for researching Maltese ancestry in Egypt, yeah, its painful. There are some good resources out there. You might want to contact firstname.lastname@example.org
; he has a data base of Maltese in Egypt so he could have some info for you.