Cutting out members of Shirley’s family for dramatic effect to make that story work would be the logical next step in order to make the movie’s friendship story work, even if it wasn’t true to character for Dr. Donald Shirley.
Therefore, learning that perhaps Tony Vallelonga and Donald Shirley maybe weren’t the best of pals as the movie implies would not be a huge shocker.
But as is the case with many biopic movies, learning the whole truth may require some research.