I think big brother's hives is also a supernatural sense just like the oldest sister's. Hence why it was specifically mentioned that he even had a relapse during their parents' funeral. Come to think of it, every sibling seems to have this sixth sense. The past Ginji made a reference to Akira being able to see ghosts, and then in the present day, Kaede "heard" them as well. Ginji obviously had some form of it as well, since he was able to tell that Akira was able to see them too. And since he had always been a creepy person ever since childhood as per Akira, it is possible that his supernatural sensitivity was actually the strongest.
Since Ginji specifically cursed his four siblings and likely used himself as a sacrifice, in addition to all the children having bits of supernatural ability, I think what happened here is that their mother was someone with a very strong supernatural aptitude who perhaps defeated some nether being long ago. Ginji's experiments with his own ability went too far and somehow allowed the vengeful being to possess him, who now targets all the remaining descendants of its old adversary.