What could Kishore probably do? He tried to speak up/step ahead and Kala stared him down. He is afraid his son is going to have another "accident" and I can't blame him. Even if he asks Dutta for help, why would he believe the brother in law more than his sister? And Dutta has already lost it, pointing now at yet another person close to him, that could lead to a total disaster.
I think he tried to stop the wedding because by leaving the house, Naku was basically save and though I'm sure he wasn't proud of himself for staying quiet he was okay with it. She was out of Kalas radar, away from Duttas anger and so on. But Dutta had to drag her in again. To make her and his own life a living hell.
Absolutely true. Kishore is afraid of what Dutta might do, just like everyone else. Plus, he is holding a loaded gun; it's a miracle he didn't shoot anyone dead.