It should be obvious to Gulaal, Dushyant and indeed the whole household that Kesar harbours a strong distrust and dislike for Dushyant - why has no one wondered or tried to find out what caused it?
G & D know Kesar hates D, G & D know D had killed someone very dear to Kesar, D also knows Kesar is investigating the killing. How come they can't put two and two together and figure out that Kesar must suspect something about D's crime which is why he is behaving like this towards D? Elementary, I should think.