I have twin boys I was set up by a syndicate through the mother who asked for 100 thousand dollars for the children to be legally mine I am biologilly father and have d ans a to prove it when I refused to pay she attacted me and my friend with knives and we were slightly cut about defending ourselves she was arested and locked up I have had custody of the twins for 9 months and have aussie passports and citicenship for them granted in cambodia by aussie immigration in cam I am a aussie citicen living and working for the world bank in cambodia I want to change their last names to mine as the mother was smart enough to name them in vietnamese what can I do

Were the twins born in Cambodia? If Cambodia has the equivalent of birth certificates, you could check with the Cambodian authorities about changing their birth certificates.

But an application to the Australian courts to change their names would probably make more sense. Find an Australian lawyer to help you do that.