OOC:
Given that Eidolon is an Exorcist like his son Geist, this means that Eidolon can communicate with demons and spirits and such. During his life when alive, Eidolon often made friends out of the various ghosts and spirits wandering around House Grace, and sometimes his own servants would be ghosts. He’s got ghosts helping with cleaning and providing lovely music for guests, including a harpist that likes to play every morning.
Geist, during his younger days, often hung out with these ghosts. He was more comfortable with them than with live people at times. It got to the point that the ghosts themselves tried to encourage him to go out and hang out with live people, too.
Most of the ghosts got driven out of House Grace post-Geist bringing Revenant back by sealing his soul into a suit of armor, because the Orthodoxy pretty much stormed the place trying to silence Geist for stuff involving the Great Plague and such. A few ghosts still managed to remain in House Grace despite their efforts, however, and they still are in House Grace post-Bravely Second when Geist and Revenant return home. It’s kind of a headcanon of mine that Geist and Revenant went back to their old home post-Bravely Second, because they would have reconciled with Pope Agnes and stuff by then.
The ghosts of House Grace don’t ask for much from anyone that visits—just don’t be rude to them. They’re quite nice, actually.