Since it seems like it's possible to do, I'm probably going to replay chapter 3 a couple different times as it looks like you can just fudge some numbers at the beginning of the game to try and get the different endings but stay on everybody's path for the first two chapters.
I think the sis and Christina are the hottest two girls in the game, but I'm really hooked on sis the most.
Man I could try the harem ending but I would also like to do the sis & Ashley ending just out of spite to be the man that the MC's dad never could find himself to be haha.