I've played this from the beginning. The story focused on Melonie, the twins and the wanna be actress had some, and the secretary was nil...80% Mel/Tiff, 20% rest.
Then he took nearly a year to re-do the game, leaving Mel/Tiff about the same, and focused on the others instead. The story was to focus on revenge on Mel, but the Dev felt the story he had in mind was too dark, so he decided to focus on the other characters, while he tried to make up his mind on what he wanted to do with the Mel story path.
So yea, the other girls to me are side characters that are being used to fill in the gaps while the Dev decides what he wants to do with the main story path.