And I can now confirm that he was indeed married to Queenie Vassar (1870-1960). She was born in Glasgow and first went to the United States in 1884.Mike,
Joseph Bridger Cawthorn is the man. He was born in New York in 1868 and began acting on stage at the age of four. His parents were both from England, where he then began performing in the musical halls there at the age of nine. He then returned to the U.S. where he performed on stage in variety shows and, later, motion pictures. According to the 1910 census, he was living on Bangs Avenue in New Jersy. His wife, Queenie, was born in Scotland and was an actor as well.
In that case; on the 1901 Census he was staying at the St. Ermin's Hotel, Westminster, London, age 33, single, and gave his occupation as Actor, born United States. Whilst four lines above him may well be his future bride (?); Queenie Vassar, 30, widow, Actress, born Scotland. (If you let me have your email address, I can send you the Census return.)
And he was living in LA in 1930:
Name: Joseph Cawthorn
Birth: abt 1868 - location
Residence: 1930 - city, Los Angeles, California
The California Death Index, 1940-1997 Record lists his death in 1949:
Name: JOSEPH BRIDGER CAWTHORN
Birth: date - NEW YORK
Death: dd mm 1949 - city
Joseph Cawthorn was born on 29th March 1867/8, and died on 21st January 1949 following a stroke at his Beverly Hills home. He had moved to Hollywood in 1927, to begin a career as a character actor. There's a good resume of his career here, though no mention of his having played any sort of concertina.