I don't know about Australia, but in my jurisdiction any illegal contractual clauses are unenforceable. If the law says "X is forbidden" and the contract says

I don't know about Australia, but in my jurisdiction any illegal contractual clauses are unenforceable. If the law says "X is forbidden" and the contract says "employee agrees to do X" then the employer has no legal recourse to force employee to do X. Point 2. is the usual on-call, and it's still regulated (in my jurisdiction) by mandatory rest periods during which a person is legally mandated to not work.