Can mainlanders go to Hong Kong to buy land and build factories? Can I buy land and build a house in Hong Kong? My family wants to immigrate to Hong Kong. what can I do?

No, you usually have to immigrate to other countries before you can immigrate to Hong Kong. Mainlanders can't immigrate to Hong Kong unless you are talented.

First immigrate to a small African country, and then invest 650W to buy real estate in Hong Kong.

If you have money, you can immigrate to Australia with a visa132/1119 and then move to Hong Kong. Will not involve the trouble of tax and financial audit. It's easier to operate.