I don't believe all's as it seems with Yeonjoo's family. I am almost certain that there's some justification for their annihilation but we shall soon find out.
At the end of the day the seme was doing his job. He did not kill the ukes family just for fun and if he did not do it someone else would have been ordered to do so.
Translator,don't listen to the hating bitches. You doing good