4. Use professional research
The only person I've heard of that researches families in Hong Kong is Ms Christine Thomas, based in the UK. Her website is http://www.researchhongkong.org.uk/
If you'd like to recommend a researcher, or you provide research services yourself, please leave a comment below with a link to your website.
PS I haven't used any of the service(s) listed here, so you'll need to satisfy yourself that they can do the research you need before any time / money is spent.