Chara and Frisk are twins. What happens if one prefers a twin over the other?

When a mishap in a reset happens and a character from another version is transported into the current world and timeline, what happens? Gaster!Sans, bad-skele-boy from EchoTale is confused to see that he had landed in a different, yet familiar world: Undertale! Apparently, in meeting with his 'original' version, they seem to be OK with one-another, UNTIL... (Thank you, @yourebluenow for the cover!) Book 2 Is here! it has the same name and cover, but with 'Part 2' in the title! https://www.wattpad.com/story/70011017-love-me-instead-sans-vs-gaster-sans-x-reader-part

Uh

You have a small secret that no one knows about. You are the only pure soul human that anyone has ever met. You keep the soul a secret from everyone. That is, until a certain skeleton decides to come... ... And one thing is for certain... He wants your soul. But he also wants you.

Frisk struggles to provide for her little sister, it doesn't help that she gets taken by customers of a bar. What will happen to small Chara, will frisk escape the gang and reunite with her sister or will the two girls perish? ~Reaaaddd toooo findddd outttt~

Monsters were freed from the underground by Frisk 10 years ago. Alphys created a synthetic soul for Asriel, and soon enough, he convinced Chara to go back to her family. Soon after Chara and Asriel were murdered, Frisk was thrown in jail for the worst crime that she didn't commit. Will Frisk survive in jail while the case is being solved without interactions with other terrible criminals, or will she die before she is saved?