So I'm not sure if someone in the first story is happily packing up the family house in the company of someone that she then tells Tsukasa has been dead two months, but that's how it looks to me. Could be her sister. Could be another relative. Other person does disappear from the manga's panels without explanation, but dammit it was other person who unlocked the house in the first place. That's a pretty solid ghost.
But then the second story has a whole chunk of action that evidently... didn't happen at all? Why the viewpoint character thinks it happened is not explained. Maybe ohh a fourth or fifth reading will cast light on the problem, as also the suggestion that Grandmother was making pacts with demons, which I'm sure is not the case. We're at levels of first- Kai-story twisty misdirection in this volume.
House of Five Leaves
Shadows over Baker St
The Wolves of Willoughby Chase
Shamans, Housewives, and Other Restless Spirits
Ocean at the End of the Lane
Novel Written on Yellow Paper