Responses
pei killed milena's family because of his obsession to milena (being one and only for her), I guess pei's family helps him back then (tao was there, idk the others) and belly survived coz he's not in the house (late), pei's family is holding belly's hostage while milena runs away from russia to korea. so when milena came back, she's seeking revenge (and save belly)

I read it a bit haphazardly due to the language barrier. Could you please explain why Milena killed Pei's family and why Belly was at Pei's house? I didn't quite understand that part.