You can enter the departure area as long you've got a valid boarding pass. I have done that with arriving 9pm and connecting flight 9am next morning without a problem.

However, you are not allowed to use the lounge by rule by yourself. But since your family is flying in F, that would not a problem either.

You can enter Hong Kong later, check with the ladies at the lounge and since you've got more than whole day, it will be alright.