Update: I heard from Uncle Jack, who ID's the people in the picture as follows:
First row: John J. O'Hara [partially obscured] (his father/my great-grandfather); Harry Kunze (husband of Helen Quinn Kunze); Charles Kunze (Harry's brother); Bobbie --- Quinn (wife of Martin Quinn); Lillian Kunze --- (Harry's sister)
Second row: "old Uncle Mark" aka Mark Gillen (brother of "Nanny" aka Mary Gillen Quinn, who was my great-great-grandmother); Mark is holding Lillian's daughter; "Aunt Annie" aka Annie Gillen (Nanny's sister); Helen Quinn Kunze
Third row: "little Harry Kunze" (Helen and Harry's son); Terry Quinn
The family that ties all of these people together are the Quinns. Mary Gillen (sister of Mark and Annie, among others) married Hugh Quinn. Their children were Agnes Quinn (m. Bill Maines), Mary Quinn (m. John O'Hara), Helen Quinn (m. Harry Kunze), Martin Quinn (m. Bobbie) and Terrence Quinn (m. Alice, I believe). Some of these Quinns are pictured above, as are members of Mary Gillen Quinn's natal family and Harry Kunze's family.