I wouldn’t say he’s a shitty brother, just because he left. It’s not his fault that he had no power to protect mc. At least we still see that the brother cares for her.
To be honest I don't really mind the brother but,the Suspect is definitely the Empress like she probably got help like dis.The Maid was already there before the whole incident and since the Stepmom can't really go out or talk to anyone obviously someone and she is on House arrest meaning she will only get food and shit.So the fact that that maid must've been recommended to her by the Empress must mean she's been getting letters from the Empress through the Maid cause she hands out the food to the step mother rigth? what y'all tink
This is just my theory but it's the queen who is trying to kill the FL. It can also be the demon king or some one who wants to marry the demon prince. It just can't be the brother, but he is a shitty brother nonetheless. I understand that he had no choice but to leave, however he could have atleast done something to protect his sister.