the package only covers for 2.
you would have to pay for the 3rd one in your party.
i haven't read the package details lately.
i would assume it would be for the entire stay.
you could break it up and book half with the package and the other half of your trip room only.
i have not found that booking the packages is the most beneficial way to stay onsite.
if you break down the costs of the room, park tickets and the daily breakfast, you should come out ahead by purchasing everything separately.