i don’t understand anything that’s going on the plot is so weird for me

I don't know which part you're talking about but the sister and their household, Adam's family that's been happening will be explained on the next chapter which is chp 15. They're only following the story of the game. The FL is just trying to find a better ending route for the main character of the story which is the guy in the prison tower. Just think of it as a game with no skip button for the main story but you can do whatever you want and gather some side quests but it has effect.