I saw another CDV of what appears to be the same brothers, with similar outfits and different hairdos (probably a couple years older). This one is labeled “Willie & Freddie O’Brien”. I did a quick google search on their names and it turns out they were well-known circus performers, part of Barnum & Bailey’s circus, among others. A brief bio of their father (from Olympians of the Sawdust Circle):

O’BRIEN, FRED. (1848-April 28, 1881) Champion leaper. Native of Buffalo, NY. Lake’s, 1869; Dan Rice’s, 1870; Rice’s Paris Pavilion Circus, 1871-72; P. T. Barnum’s, 1872-73; John Wilson’s, San Francisco, January 1874; Cooper, Bailey & Co., 1876; Great London, 1875-77; with wife and sons, Freddie and Willie, Orrin Bros.’, Havana, 1878. Wife was a slack wire artist and his 2 children performed on the trapeze. With P. T. Barnum’s, Madison Square Garden, 1881, was injured in a leaping double-somersault over a number of elephants. Died aboard the steamship England en route to Liverpool as a result of those injuries, age 33. Remains were buried at sea.

O’BRIEN, FRED, JR. Acrobat. The son of leaper Fred O’Brien. Three Melville’s & Co., 1889; general superintendent, Price & James, 1897; principal clown, Cooper & Co., 1897.

O’BRIEN, WILLIAM. Acrobat and leaper. Son of Fred O’Brien. Howes’ London, 1877; Cooper & Bailey, 1880; Howard Bros.’, 1888; Charles Andress’, 1888; Robinson-Franklin, 1897.