Yes Samrat along with Virat and Mohit have failed in their duty as a brother to Devi. Specially Samrat and Virat with their extensive training and knowledge should've seen the signs that Devi tai is being deliberately drugged and locked inside. They should've also raised their voice when Devi wasn't allowed to participate in their family events and was kept locked in the room.
Samrat also failed big time as a son. What he did to his mother, the pain the uncertainty in which she lived with for one year is unforgivable! No redeeming him there. Another thing that can't be redeemed is him leaving his duty towards his country for a heartbreak. There are many ways he could've gone about doing that but he chose the easiest route. I don't think anyone's refuting these things, he is 100 percent guilty in these two matters.
Coming to Samrat being there for Sai and people praising him, he totally deserves every bit of that appreciation. Cuz he did something that no son had ever done which is shut up that criminal family when they start to spew their shit. He's not become a blind cheerleader for Sai just cuz he thinks Sai is mahaan. He clearly noticed a pattern where Pakhi taunts Sai for something unrelated and the family starts their Sai is jungli rant.
What I liked about Samrat in that precap is not that he is shouting at his wife or that he's teaching her a lesson, but something that should've been asked from Pakhi this entire time; what the hell is her problem with Sai? Even if Chavans are quiet she will start her anti Sai tirade by herself. What happened with Sai is not normal today and on top her husband has zero guilt on this matter, Pakhi being a woman not taking the right stance and instead supporting the wrong party could've triggered him.