Family dispute on property.

Respected all My grandfather bought a residential house around 25 years back in rajasthan. He got registered it in the name of self and my grandmother in equal portion. My grandfather has 4 sons and two daughters. My grandfather had prepared his registered will and of his share in favour of one of his son whom have been living with him till now. My grandmother also wanted to give his share to that son but since she was paralysed she was not able to visit registrar office thus the beneficiary son written his will on plain paper and she put his thumb impression on it. Last year grandmother expired now other sons want their share in full house while grandfather still alive. Out of other three two were already seprated from our family business and property there share at that time (arount 15 year back )were fully paid while third one is in partnership with beneficiary son. Now they (other three sons ) are intimating us for legsl suit if there share is not paid. We dont have proof of settlement of their share earlier but our family friends and relatives are in our favour. One important thing i want to tell that once both gf and gm signed a stamp paper stating that house will be of all the 4 Sons but will is prepared after two year of that. The original stamp paper they are having now. Kindly advise whether they succeed or not.