Paternal Aunty property division

My grandfather was a self made millionaire. After marrying his three daughters and son, after all his grand kids were born he left all his properties to my dad and about 1 acre of land to all his three daughter as will, but he had an accident and 3 days before his death in 1989 he revised his will to give all the property to my dad, this was witnessed, and registered. My dad and his 3 sister were all born before 1955 in Tamil Nadu. At my grand dad funeral there was a dispute and my dad didn’t speak to his sisters for 10 years and we have reconciled. My dad’s older sister passed 5 years ago, unfortunately his Middle sister son died from cardiac arrest this year and his middle sister has send us notice through her lawyer, her other sister and nephew and nieces don’t want part of this, she had send them notice for information. We tried to negotiate, but she is asking for 1/3 acre of land. I think we have Commercial shop in that part of land and I spent 35 lakes adding 5 more shops this year, Will court stay order freeze my income here?? Currently all the property are in my dad name and I have built new house in the other end of the land total 4 acres. Is there statutory period contest a will??