We don't know how much time has passed since boon ok sister was labelled as a spy. Maybe she was little back then. Otherwise I can't think of any reason why Seung hee keeps defending her.
I don't think so. Everyone keeps reminding boon ok that her sister was a spy of the north. And Seung hee was also forced to say that she was a spy sent by the north. Do you think these are simple coincidences. Also we still haven't seen the half bent photo hidden by Seung hee. I believe it is her photo with boon ok.
Can someone explain me how the guy who killed the director is still alive?
If you are talking about Yoon Gwi Nam. Then the vitus has mutated in him. I think it is because of his strong resentment (feelings) at the time he was bitten. Some sweet home kind of plot armor.
If you are good at maths it is easily possible. I posted this comment exactly after 7 hours the show was released. And the show is of 55 min nearly per ep considering you remove the credit scene of 6 min.