Actually it would be funny if Chihiro is the host for Demeter, and the goddess is the mother of the other 6.
Now that is tricky. How can all the 7 goddesses love Keima without making the harem look incestous?
I am inclined to think that there are 7 goddesses instead of 6. Demeter was left behind so there will still be a goddess around to watch the land.