blackmail from the other party

around 30 yrs ago when my father died my eldest brother sold a few of my father's properties and shared the money within our 4 brothers excluding my eldest sister who was married by then.The left over properties were sold in due course recent being at 2006 exempting my sister signature.My sister was asked if she want's share in reply she demanded some which i have paid(more then 10,000 approx) but haven't taken anything for writing from her as she was not present and i have sent the money by his son's hand. Now from past few months her sons are constantly blackmailing me for giving the whole money of every land deal and threatning for moving to the court where i would loose my job along with the pension.I am an govt. employee on the verge of retirement not being physically well i am fully tensed .hence i request you for a possible solution and possible threats and what i should do now? is my job really gonna go or would i face any criminal charges or should i agree them paying outside the court.please help me!!!