Ankush and Shailesh can pure evil. There's much much more to their evil deeds than what is being shown.
But what is not clear enough is that, how can they keep him(the king) for so long inside that devdi?
It is clear from his personality that it is none other than ritik as raja himself which further proves that he's ritik's father and the owner of haveli, which was somehow taken away by ankush & co.
And I think shesha's past is also connected with the king. He might have betrayed her that's why her eyes were filled with so much hatred when she was talking to His picture.
Further, today ankush said that the king was very important for them, so he can not be killed. I don't think he's 5th culprit either.
Though this epi somewhat solved the puzzle but still many pieces are missing.