Since I posted this message I have located the graves of my great grandparents. I have also found our that my g-grandfather came to Australia as a teenager with his parents.
Their graves are at Pinnaroo cemetery in Brisbane. I have also been in contact with someone whos husbands family are Nittis' from Kastellorizo. I'm waiting to hear from her again as to whether it's the same family.
If you could help that would be fantastic.