He was married to Phyllis Jean-Jacques, born in Germany in 1923 or in 1925 (d. 2004), whose sister had kept in correspondence with William via mail. After their relationship had begun, William, Phyllis, and Bridget sought anonymity in the U.S. William and Phyllis married in 1947 had their first son Alexander Adolf in 1949. They would later have three more sons, by the names of Louis (b. 1951), Howard Ronald (b. 1957), and Brian William (1965).
William died July 14, 1987 in Patchogue, New York, US and was buried alongside his mother, Bridget, at Holy Sepulchre Cemetery in Coram, New York. Phyllis died on November 2, 2004.
Howard Ronald Stuart-Houston, a Special Agent with the Criminal Investigation Division of the Internal Revenue Service, died in an automobile accident on September 14, 1989 without having had any children. Howard Ronald is buried at Holy Sepulchre Cemetery in Coram, New York. It has been said that these three have vowed not to have children themselves,[ and none of them have married. However, Alexander, now a social worker, has said that he knows of no such pact, and that if it had been made, it was made by the other two brothers without his involvement.