if it is believed that a deceased relatives will and documentation is fraudlent, how is that researched?

In 1870 my great grand father his brother and a cousin bought 167 acres in east Texas. My mother one of 3 children of the 5 uncles was told that her grandfather gave as inheritence all 167 acres to one Uncles unadopted step child. MY mother heard many conversations amongst the family that each brother (her Uncles) would recieve a portion of the property at the death of their father. Now an attorney is claiming that Great granpa deeded the entire 167 acres to this woman who is no realtion to the family, but was taken in when her mother married my mothers uncle.Is there a method to verify/validate whether or not the documents claiming that she inherited the entire 167 acres of the property are legitimate?