Yes, you can definitely eat them. They are so hard, though, that you can literally smash them onto the bottom of a pan or counter and not make a crack, or whack them on the edge of a bowl and just make a huge messy crack that gets shells all mixed up in the egg.
Here's a good way that my husband figured out to crack them: Hold the egg in your hand with the big end sticking out. Take a table knife and strike the end of the egg, as if you were going to slice off the end.
This will usually make a crack but not pierce the inner membrane. Take your fingers and remove enough shell pieces so the yolk will have room to slide out. Then tear open the membrane and dump the contents into your bowl or pan. No shells in the egg this way!