the number you need is listed as the "hotel confirmation number" and it is right under the hotel you booked. You can't use the orbitz record locator number. The other one will link the reservation in your
mde.
Wdw can't add people to your reservation. Orbitz will have to do that by calling wdw directly. Try back again and tell them to transfer you to someone who can add people to the reservation (if they tell you that they can't do that). I have done this twice recently.
Make sure that they don't try and charge you extra if these are kids. You have to let them know that wdw doesn't charge for children and that they just need to be added.