The helicopter itself is 30 tons, leaving you 30. But 60 is the max takeoff weight. The max weight it is actually designed to operate at when carrying the maximum load is about 55 tons. With 30 for the helicopter itself, that leaves 25 tons for the load.

A container can be up to 33 tons loaded, so the heaviest will be beyond that helicopter (at least of you don't want to push it past its safe limits).

I assume that the heaviest containers are on the bottom of the stack, and that most containers aren't near the limit, so it could probably unload a substantial number of them.

You can't take only the containers at the ends, however, because the uneven weight would cause the center of the ship to collapse.

Not so sure about that collapse, the keel of the ship is currently supporting all of that weight and seems to be holding up just fine. It's essentially a suspension bridge at this point, but I agree that it is probably better to unload evenly, however, that will add another very substantial time penalty. If the ship would break (which I have no idea at what load imbalance that would happen) there would be a delay a lot longer so it may be worth it to play this extra safe. But there is a very large amount of pressure on the people there to get this resolved.