Andrew, my best guess is the photo shows your relative Joe Grenon standing with drivers Bob Burman, Louis Disbrow, and Jack Tower at the Merrimack Valley Course near Lowell, Massachusetts in September 1909. Grenon, Burman and Disbrow all drove Buicks in these races.
Joe Grenon (AKA Joseph Grinnon or Grennon) drove a Buick-10 in the Merrimack Valley Trophy Race on September 6, 1909 and finished eighth. His 1909 AAA statistics are listed under Joseph Grinnon with a html link of "GrennonJ".
It is very likely that the car behind the men was Robert Burman's #4 Buick which finished fourth in the 1909 Lowell Trophy Race. Burman also drove a Buick in the 1908 Garden City Sweepstakes held on the Long Island Motor Parkway course and a Marquette-Buick in the 1910 Vanderbilt Cup Race.
Louis Disbrow drove a Buick in the 1909 Merrimack Valley Trophy Race and finished 5th. In Vanderbilt Cup related races, Disbrow drove a Rainier in the 1908 Meadow Brook Sweepstakes and a National in the 1910 Vanderbilt Cup Race.
Jack Tower was involved in racing since 1901 and frequently served as a mechanician for many big races. Although he did not participate in the 1909 Lowell Races, Tower was later on the Buick team in 1910 as the mechanician for Bob Burman and then with George DeWitt. He also drove the #26 Jackson in the Inaurgural 1911 Indy 500 Race.