We find it impossible to crack the almond shells on our almonds from two trees we have. What are we doing wrong?
I don't think you are doing anything wrong, some almond shells can be notoriously hard, depending on the species.
Maybe you are used to having soft shell almonds and your trees produce some hard shell variety.
Soft Shell Almonds
Hard Shell Almonds
Make sure they are ripe and dry enough (no fresh pulp around it), greener shells are generally slightly sturdier and harder. They tend get a bit more brittle/crumbly when they get ripe and less humid, after the soft skin falls off.
When I was a kid I used to eat fresh almonds straight from the tree during summer vacations at my grandmother's, and the only way we could crack the shell was literally hammering it with a small stone against the ground, and specifically on a hard surface, like a curb stone or something.
And even then it requires some skill, because hitting too softly won't crack the shell all the way through, hitting too hard will smash it completely crushing the edible part into a mush.
To do it at home a regular "pliers shaped" nut cracker should suffice, though it will require strength and more pressure then say most walnuts for example. If you aren't afraid to break a door, a common workaround is to put it near the hinges, between the jamb and the frame and slowly close the door, that should crack it open easily.
Be warned this can damage the door, break the hinges, and dent the wood. Don't blame me for damaged property! ;)
I think the writer may be referring to the outer husk that is the issue. I have two large trees as well. Here in Florida, the almond husks do not split on their own revealing the inner shell. They may as well be coconuts trying to get inside. Without a vise or similar for leverage and a saw, good luck opening them. If you can manage to remove the husk, then they are no different than other almonds. For me, the trees are pretty. I've long since given up on trying to get the almonds.