Blank cheques of dead person

dont worry the second party is also in fault, so can not take any legal action aginst you

He cannot do anything with the blank cheques unless they are dated to before your grandfather died, and even so, cheques have a validity of 3 months so it is his fault if he did not encash them. He cannot fill in details which would make the date of the cheque appear to be after your grandfather's death, and since he died in 2016, anything prior would be invalid. However, he can bring a recovery of money suit against you unless you obtained a receipt from him for the cash you paid. 

Sir do not worry, there will be no problem. 

As I stated before, even if the cheques are undated, they can only date them to before your grandfather died. Cheques have a validity of three months, so if they did not encash it in that period, then it is their own fault. 

Furthermore, even if you do not have a receipt, in such circumstances they would not initiate any case against you.

Finally, the blackmail wont work because those cheques are now worthless pieces of paper since it has been more than 9 months since your grandfather passed away. If they continue bothering you, file a police complaint against them and let the police know that they are attempting to blackmail you with your grandfather's cheques. However, I would leave that as the last option, as no harm can come to you from those cheques. 

Properly advised by Saumya ji, 

you need not to worry, however a civil suit for recovery can be filed against the legal heirs of your grandfather but chances are on lower side but as a precaution you are adised to get reciept, if possible.

also clarify whether the cheques are in his name or in the name of his grocery store? is it one cheque or more than one?