missing sisters

i am looking for my two half sisters, allison & karren. I beleive that they could be in there late 40's(not too sure) living somewhere in australia. Dont know what their last names are now but their mum is called Celia, they had the same dad as me, he was called Rodney Bayles, he was born on the 3rd june 1935, died 8th april 1993 in guernsey. They may not know of his death. any help would be appreciated.