If you look at the wikipedia page for Sam Walton, the founding looks a little more nuanced:
"Walton went on to open more Ben Franklin Stores with the help of his brother, father-in-law, and brother-in-law."
Sam Walton's autobiography mentions that his father-in-law provided the initial capital (that was about it), and his brother played an insignificant role (like buying things from suppliers). His brother, who was younger, was more of a helper while Walton built his first store (a Ben Franklin store that he later sold and started Walmart on his own based largely on his Ben Franklin stores).
and Wikipedia. I went through most of the list. It's right to me.