
so people say its not incest and i read all the chapters available but im a little confused. the girl was born and the mother also had a demon child(the son) whom she did not give birth to? where did the demon child come from then? when she prayed for a son it popped up? im a little confused and need an explanation T^T

There seems to be a line insisting that the demon slept with the mother after the coffin came to the castle. "9 month after the coffin came, the mother gave birth" or something like that. I'm assuming that's the demon's child. the mother of course didn't want the demon child. so she made a wish to that coffin man (I forgot name lol), wanting a human son. so that coffin man granted her wish and magically the demon child became a human child. but as told by the mother and even female lead, only bad things come when you make a wish to that coffin man. tbh there's many things that are not explained yet so guess we have to wait for more chapters to understand everything.

I don't know exactly when she conceived the demon child, since it's hard to tell, but I think she was pregnant with Annette but as she had no way of knowing if it was a boy or a girl, she wished to have a boy, so the demon boy was conceived sometime during her pregnancy with Annette, afterwards she gave birth to the twins but it turned out that he was an actual demon, so she made a wish to turn him into a human baby so that's what we have right now.
As for the incest, it's really up to you to decide, one the one hand: they were born and conceived from the same womb, they look like twins (in the demon's human form), they were raised as siblings from birth, they grew up together, and most importantly, they recognise and acknowledge each other as siblings, which in my opinion, qualifies this to be incest.
But on the other hand, they were not formed from the same sperm, they are not even of the same species, and (I'm not sure if this is true since I read it in a spoiler quite some time ago) apparently Johannes always knew what he was, so he knew they weren't fully related even though Annette did not and considered him to be her twin brother.
So I guess you can just take your pick of whichever one you agree with more, in the end of the day it's still kinda messed up, but we enjoy it regardless.
my knees hurt for him :c