I believe the red on she's talking about is the ml. Since he's the 2nd prince and in the cover, the boy had red eyes
According to Tia's flashback he might be sane... but then again, he did fxck up his brother to get the throne, so I say that he's rational, then again, during those days, it was normal to kill for the throne.
I think he's not the empress' son coz she loathes him. His got black hair and red eyes.
Hmm..maybe because I've read a lot of manhwas, I forgot some detail and was confused. Sorry for the spread of wrong information :>
So it seems the total family is full of psychopaths so far....
Let's hope the red eyed son they spoke about isnt also insane.