Ira and Alok, without a doubt.
All the other parents at least had some excuse or the other they could hold on to like narrow-minded, orthodox backgrounds, circumstances, illiteracy, general mean nature, the rural mindset etc.
But Ira and Alok both come from good families with well-educated backgrounds and broad minded and modern views. They have given their kids the best in life like excellent education and all materialistic comforts yet when it comes to basic child-rearing skills they have failed miserably with regards to Sanchi.
Being the only girl and the youngest in the family they went overboard in their pampering, fawning over their little "princess" and heeding every whim and fancy of hers without any limit, never instilling any values in her. As a result she's grown up thinking that anything and everything is hers for the taking without a proper sense of right and wrong.
They seem to live in some kind time warp where they have forgotten that their daughter is a grown woman and accountable for her actions now, and still go on treating her as a bachchi. Then why, pray, were they thinking of getting her married in the first place if she was still a child and all that she does is just her bachpana! Why not wait till she has "grown up" before she's off setting up a family of her own?
They are definitely those set of parents who fear above all a meltdown or tantrum by their children and go out of their way to pacify them. The way they were acting fearfully before telling her the news of the breakup as if she'll explode any minute clearly shows that it wasn't the first time she's done thod-phod when she didn't get her way.
And even now instead of consoling her and trying to get her to move on from this fiasco Ira is planning on revenge on the Singhs! Oh boy, are they in for a major shock when their precious princess's true colors come out into the open in front of all! Would love to see who Ira and Alok would blame then.