You can read chapter 11 here and this is original website so it's released earlier compared to here and mangadex
https://leviatanscans.com/comics/852376-not-just-anybody-can-become-a-villainess/1/11
........
Ok so I looked at the raws, and the comments talking about how their not actually siblings may be true. So one of the devil boxes was cracked open and the devils wing was still in their unlike when Mc did it. Which may mean that if the male "twin" broke it he could possibly not be related as it only works for the true bloodline
I'm pretty sure she made her demon dude start a fire to avoid hanging out with the fish's lol ( ̄∇ ̄")
She’d be watching on a corner saying yes, now run.