Two sailors

I am looking for two ancestors that I think have been sailors. One ended up in Shanghai and the other one in Australia. The one that ended up in Shanghai was named Haakon Randby. He got married to a Russian woman and after she died he remarried a Chinese woman. After what I’ve been told he had a kind of hotel in Shanghai and he was well known by Norwegian sailors. He was born 1881 in Hammerfest. From postcard posted from China 1909 I assume that he maybe was settling in Shanghai around that time. The other brother was Emanuel Rudolph Randby. He was born 1863 in Kristiania. I know from a letter from his daughter to my grandfather that he lived in Australia. After what I know my grandfather never answered the letter so I do not have more information than her name and where she lived many years ago. The letter was sadly not dated and we just recently recovered it . The daughters name was Sylvia Franks and she lived in 409 Darling St. Balmain that I found out is in Sidney Australia. So if someone her have tips on how to track ancestors in Australia I will be grateful.