Will by Fraud

Hi, I seek legal advice please on below mentioned case. An Old Man who had chronic disease since 1995 suffered brain hemorrhage attack in the year 2003 followed by another major attack in year 2013 which had really shattered his physical & mental state of health. He was in COMA thrice during his lifetime & had also lost his memory twice. He was bed ridden for 6-8 months post which he passed away. Throughout his life he was looked after by his elder son & his family. The younger son lives abroad. He made his 1st Will which was favoring both of his sons wherein they had equal share. But old man’s younger son in the year 2014 hatched a plot & took advantage of the old man’s mental state & got the will amended i.e. everything goes to him. He had also arranged a government doctor certificate to prove that the old man is mentally fit. He also instigated the old man to the extent that the old man told his elder son to leave the property & stay at another house. The old man was made to believe that his elder son would kill him which was never the case. The elder son resisted but was finally told to leave by the court under Senior Citizen Act. Once the elder son left the house the younger son did not made any special effort to look after his father & literally left him to die. Although the old man was getting treated at PGI for his brain hemorrhage attack since 2003 but the younger son for his own convenience & for the sake of formality took him to a local nearby private hospital which doesn’t even have any expert doctor. This resulted into the sad demise of the old man within a time frame of just 3 months of elder son leaving the house. The property in question was constructed jointly by the old man & his two sons. I suspect that even the father of the old man had contributed towards the property although the old man has always claimed it to be his own property self-acquired. Under these circumstances can the will be challenged & what are the chances of getting the Will quashed on above mentioned reasons? Can the elder son seek justice who has rendered seamless services to his father? How will he get his due share in the property wherein he had spent lot of his hard earned money towards construction & renovation? It is a case of getting the will made under undue influence & the old man was not even in a stable state of mind. Most Importantly – The Will has couple of important mistakes in it. The old man’s statement & declaration in the WILL & Courts is different.