Transferring from Bank of China in Hong Kong to my own Bank of China in China is quite smooth, with no fees and normal exchange rates. After the funds arrive, I can search for foreign exchange in the app, and I can exchange it to use normally. This is considered cross-border transfer, which arrives in one working day, so exchanging USD in the future is not as risky as I imagined.
Another method is to have your family member apply for a domestic Chinese bank card. You can then transfer to their card, effectively giving you an additional $50,000 exchange quota, which is more than enough for family expenses.