Thomas Martin Einstein
Albert Einstein had three children, Lieserl Maric (1902–1903?), Hans Albert Einstein (1904–1973), and Eduard "Tete" Einstein (1910–1965), but only Hans Albert is known to have married and had children. Hans Albert's only biological child to survive to adulthood was Bernard Caesar Einstein (1930–2008), who was a physicist and the father of Thomas Martin Einstein.
Elsa Einstein
Elsa Einstein (18 January 1876 – 20 December 1936) was the second wife and cousin of Albert Einstein. Their mothers were sisters, making them first cousins, and further, their fathers were first cousins, making them second cousins. Elsa had the surname of Einstein at birth, lost it when she took the name of her first husband Max Löwenthal, and regained it in 1919 when she married her cousin Albert.