I need help with the HSC!! (NSW-AU)?

It doesnt matter whether it is a family thing or a holiday - unless it is urgent like you have an operation scheduled (not a member of the family - you) that cannot be changed (and you have to be able to prove that) then you will have to resit the HSC next year. Completing the HSC is an OPTION it is not a necessary exam. Many students do not completed year 12 or sit the HSC. You will just need to complete it next year - there is no shame in taking 2 years to complete the HSC - and it will matter not one iota how old you are when you complete it.