It's not necessarily immunity to genjutsu, more just that it's easier to break out of. If none of the consciousnesses see anything wrong, then none of them will be trying to break it.

As for Kurogane, he has no outstanding abilities aside from being made out of earth and his mobility; he's tougher depending on the materials he takes, and can regenerate as long as he's touching the ground. If any part of his body loses contact with the core, it will return to its normal state. As a result, unless the material is stone, he cannot throw his sword without it turning into simple dirt or sand. With his "teleportation", he moves through the ground by taking the material in front of him as his body and immediately replacing it as he moves. Therefore if his destination is boxed off by something not made of earth, like wood, and there isn't a hole that the core can fit through, Kurogane will not be able to reach said location. Number-wise, I've reduced it to one.