Andrew is the youngest of three children. His older brother Simon Sidamon-Eristoff is on the board of many charitable and non-profit organizations and Of Counsel to Washington DC-based Firm, Kalbian Hagerty LLP, where he specializes all aspects of doing business as a charity. Andrew Sidamon-Eristoff is the son of the late lawyer, government official, and environmental advocate Constantine Sidamon-Eristoff (1930–2011) and Anne Phipps Sidamon-Eristoff. His great-grandfather, Henry Phipps, was a partner of Andrew Carnegie. On his father's side, Eristoff is a grandson of Prince Simon Sidamon-Eristoff (1891–1961), a Georgian military officer and a scion of the noble Sidamoni-Eristavi family, who emigrated to the United States after the Bolsheviks invaded Georgia in 1921, and married Anne Tracy, a descendant of John Bigelow, an American lawyer, editor and diplomat in the mid-19th century.