They're all different characters, minus Amelia. That's why they all look different except for the pink haired girl. The girls from the previous game all have minor roles in the story and aren't playable but do have their own h-scenes.Blonde one's hair style is different, green one's tits are smaller and main girl completely different. They didn't touch the pink haired girl at all. Her design was probably majority's favorite(including me ).
Link?The original translator for the prequel Jumble Jokers has started a full translation for this game as well.