You will need to handle copying the base class members one way or another.
The standard way is to call the base class assignment operator in the derived class, e.g. Order::operator=(source);
(Order::Order(source);
is incorrect, in fact your compiler should have told you as much, you cannot call a constructor on an already created object).
Your other option is to use the public / protected methods of the base class to try and set the state, but if you cannot access the base class assignment operator or copy constructor, or they are not defined / deleted, it is likely the base class was never intended to be copied in the first place.