Responses
That would be my guess(●￣(ｴ)￣●)
She might be related to the mom, and not the ml directly.
Upon re-reading, I am pretty sure the empress is his sister. It is mentioned in chapter 14 that his sister left home to create an environment where he can live comfortably. Compounding with the other reasons I have mentioned, I would be really surprised if the empress is not his sister.
Is the empress one of his sisters? His mother seems to know who she is, and is heading out to deliver punishment herself. The empress seems to know that Arel is a classless as well, which a family member would definitely know.