These are the May sisters, as someone wrote on the back of this portrait. It was taken at Hargrave Portrait Studio at 68 West 23rd Street, date unknown.

Were they three ordinary sisters posing for a family photo, or a trio of singers or actresses known in New York City at the time? Interestingly, a November 10, 1908 New York Times article may shed some light on who they were:
“Marguerite May, sister of Edna May, who is the last of the May sisters to take up the stage, will have an important part in Fritzl Scheff’s new comic opera, ‘The Prima Donna,’ which Charles Dillingham brings to New York soon.”
Could it be the same May sisters? We’ll never know.