As I understood...Shiv letting Saanchi getting her lawful punishment is only a ploy to get Jagya in jail...without that the Shekhars can't do diddley squat!!!
It's their majboori...Sanchi has to be punished for attempting suicide, because the law demands it, otherwise they would have tried to escape from this too...they know that even if the world finds out that Sanchi attempted suicide, everyone will pity her once they find out what a womanizer Jagya is and that he is now in jail for provoking Sanchi's behavior...so hisab barabar hoga...to see Jagya punished for bruising their sister's ego, they will have to go through the suicide case too, they planned on punishing Jagya and getting him locked up even before the inspector told them that Sanchi's suicide attempt is punishable, and this didn't deter them...
The issue is revenge...not to let the issue die down...not to move on...they want to take revenge from Jagya so not only law, but the world punishes him too...but the thing is, this will backfire...law & world will both turn on them when Jagya is proven not guilty. Hopefully...if abuse of power isn't involved.