According to Princess Irene (on dutch tv), prince Sixtus was actually one of the people trying to shoot them. No idea about what they were aiming to do, in case of Carlos Hugo's death it is very unlikely that his sons would have been raised by the Parma's. And I can't imagine the Dutch RF having much time to teach them about carlism...
Oddly enough prince Sixtus, who claims to bea catholic, now says that the death of the brother he tried to kill saddens him, I suppose that is some improvement

.