First, many mainland companies bought licenses in Hong Kong and then claimed to be Hong Kong companies, making precious metals. But in fact, they just bought a license, and the customer's transaction was completed in the mainland, so they must abide by the laws of the mainland, and there are precedents for problems.
Second, the company you are trading with is a pure Hong Kong company, and the transaction is completed in Hong Kong. So as long as the company is legal in Hong Kong and abides by the laws of Hong Kong, it is not illegal for you to speculate in gold in this company.
This is more complicated. If you don't understand anything, you can give me your contact information by private mail, and I will give you a specific answer.