If they are that bad from lack of use then they have probably become rather corroded and you may not be able to free them from the outside.
Though if it has been that long since you used them be absolutely certain that you have the correct key before you proceed. I have a friend who did that just yesterday. He always used the remote and the battery in the remote died.

It is unusual to have both doors and the back hatch seize up from lack of use. Usually at least one of them will work if even a little bit if they are not frozen due to cold.
(assuming your hatch has a key lock and not just the button)

If all the locks are truly seized up and a penetrating oil soaking cannot free them then there is little else to do but remove the interior door panels and remove the locks.

You may then be able to free them up with an oil bath but more than likely they will need to be replaced.

 

but its not frozen just seized