Not to be the bearer of bad news, or good depending on if you have a sibling/xxxx or not. 1, many countries don't have laws around incest, 2, some do but only forbid male v female in case of procreating. 3, and most that forbid it completely can't monitor it well enough. What people do in their own home is a secret to the general public. That aside, animated art, games, novels, etc, are usually exempt from laws since it's fiction. Meaning that Goodbye Eternity could've had family related stuff. Why does it not? Developer's vision and I assume Patreon and Gog would feel something about it. I know that Patreon does not allow it, I can't imagine that Gog would be fine with it.
PS, I have no clue what's going on here. I'm simply adding weight to the discussion. My text is not directly aimed at anyone, just some facts. Can I back this up? Sure, use Google.