Have him retain a lawyer to support his interest not one that is for the whole family and they should never have sold it the way they did. He was under duress when he signed the papers at his son's funeral. Lots of families work like this. My husband sent around $30,000 to his mother to put in the bank when he got out of the service before we got married when he got home he had no money due to the whole family (mother, brothers and sisters) using it for their personal funds. When his mother died each one of the seven was to get what they had given her and then the rest was to be divided. My husband came home with a pot and lid and a coffee table while everyone else took everything we had given her since we had been married, everything he had sent her from Germany and even the one piece of furniture that had belonged to his fathers family which is was the oldest of a half brother took who hated my husbands father. Our children have nothing that belonged to their grandparents and I resent the fact that he was owed money and we ended up getting nothing and it has been years.
I have 3 children of my own and 15 that I have helped raised when they were little and I have given them the special things that I want them to have now while I am living to be sure that my wishes are carried out.
Good luck.