The rule for dependant visas in Hong Kong is very simple and easy to understand.
In order to qualify, the family members must be either the legal spouse or unmarried children under the age of 18.
Where the principal applicant is moving to Hong Kong for work or investment, the family members simply follow in his or her wake, securing dependant visas as an adjunct to the main application, just so long as the main applicant can, as part of the application process, demonstrate that, as a family, they can all have a roof over their head in Hong Kong and will have food on the table without recourse to any kind of public assistance.
All pretty logical and sensible really.
Moreover, once the visas have been granted, the period of stay the dependants receive mirrors that of their main family sponsor exactly all throughout their time together in Hong Kong.
This means that, for example, if the principal changes jobs or immigration status, the family’s dependant visas will carry on unaffected unless the Immigration Department specifically intervene and change their limits of stay.
But it is very unlikely they will change any of the conditions though, so you don’t have to worry too much about that.