I had a bug where after the decision on how to approach Anna only the protagonist's name shows up on the dialogue boxes, no matter who is acutally speaking.
The setting is a bit bland, but with the strong limitations there is good potential to make a short but fun porn game. I mean, they didnt encounter people in 12 years, so it would be ridiculous if new characters just start popping up left and right. And if there is no one else, no one can judge or cause problems. No running away for any of the characters either, at least not if they are sane. So there is limitit potential for drama or getting off-track.
I suggest developing a 30-60 minute game where everything wraps up nicely, before moving on to a new game with all the experience you gained from developing in Ren'py and writing a storyline for this sort of game.
I think it refers to the girls being sisters. Once you corrupt them and awaken their sexual side, it's almost inevitable that they end up doing stuff with each other, with there only being three people left on earth.