I noticed so far in chapter 1 that the word "friend" is used a lot when the context seems to imply "sister" or "sibling". Is that on purpose ?
Yes. Yes it is. It's a soft censor. Some pay support will not support games showing incest and various other Fetish topics. So basically when you see LANDLADY it should be Mom...Housemate could be brother or sister. Some games get around this by having YOU define your relationships and ages of characters pregame. Others just assume we will just mentally substitute "friend" for what ever fits.