Gabriel/ Gustave Gross and his wife Ernestine Gross (nee Hornbein, b. 1882) had three children, Maximilian (1907), Viktor (1908) and Rudolfine/ Rudolfa (1911). They were born in Andrychow in Austria-Hungary (nowadays Poland). It is not clear what happened to the family during and after the First World War but Max became a Czechoslovak citizen in 1934. His mother obtained Czechoslovak citizenship in 1936.

Maximilian or Max married Irma Krauthamer (born 1921 in Leipzig)) in Prague in 1939 and they had a daughter called Gabriele (1942). Max studied electrical engineering and became an engineer and he worked for a company in Slovakia from 1940 until 1944. In that year he joined the fight against the German army but was captured and transported to Auschwitz. His wife and daughter were deported from Zilina (nowadays Slovakia) to a concentration camp in Poland (probably Auschwitz) on 18 October 1944 where they perished. Max escaped in January 1945 and went back to the firm he worked for before he was captured. In 1948 he fled from the communists and went to Sweden to work for Billman in Stockholm. In 1949 he started working for a company in France called Societé Regulateurs Industriels Billman, located in Paris, which was part of the Billman Company. In 1951 he founded his own company in Paris.

Viktor Gross moved to the UK, it is unknown when exactly, where he married Jenny Urbach in 1942 in Hampstead. Viktor Gross was naturalized in the UK in 1948. His wife was granted naturalisation in the same year.

Not much is known about the faith of Max’ parents, Gustav and Ernestine Gross, and sister Rudolfine. Rudolfine was working for a bank in Brünn in Germany between 1933 and 1939.