In 1949, Engst married Joan Hinton (1921 – 2010), a nuclear physicist, in Yan'an, Shaanxi Province, China. Engst had two sons, Bill and Fred Engst and a daughter, Karen Engst. Following Engst's death in 2003, Hinton lived alone on a farm near Beijing until her death on June 8, 2010. Their three children have moved to the United States, though Hinton notes "They probably would have stayed if China were still socialist." Their eldest son, Yang Heping (Fred Engst), moved back to Beijing in 2007 as a professor at the University of International Business and Economics. Dao-yuan Chou: "Silage Choppers & Snake Spirits. The Lives & Struggles of Two Americans in Modern China". Ibon Books, Quezon 2009, .