Wait, "imperial family"? Do you mean the Crown Prince's family (the royal family) or another one? I'm a bit confused since I don't remember that country being an empire or having an "imperial family."
It's gotta be the Imperial family. At the very least a Duke or close relative that stands to gain the Kingdom from the Prince's demise. Another option is for the Nobles who wish to limit the kings authority, but dealing with demons and killing their first born son, the Crowned Prince, is like taking a Flammenwäfer to light a candle. It makes no sense logically speaking. The only one to gain from it would someone next in line after the Prince as of that moment.
i am very worried about where the raws have ended tho... PLS PROTECT OUR PRECIOUS JULIUS??? WHAT HAPPENED??? HE LOOKED SO HURT MY HEART HURTS AND THEN SHE DIDN'T GO AFTER HIM I'M SAD I LOVE THIS COUPLE PLS FIX IT
@Sancturil Endo and Kobayashi’s Live Commentary on the Villainess, the prince from an otome game can communicate with the people playing the game high jinks ensue.
Maybe the mother of the first princess (depending if her and the prince are only half siblings) wanting her to become the next heir while Sila’s father sacrificed her in order to get a higher position by helping the rebel group. If not that then I’m not sure.
Btw Ourtzen is always a highlight in these chapters. I think I’m in love.