Mr Tisdall was born as Hans John Knox AUFSEESER, and changed his surname by deed poll on 15 June 1940 (see
https://www.thegazette.co.uk/London/issue/34892/page/4227/data.pdf). He was the son of the German Jewish artist, Professor Ernst AUFSEESER (29 V 1880 - 12 XII 1940; see
https://en.wikipedia.org/wiki/Ernst_Aufseeser) and his Anglo-Irish wife, Kathleen Isabel TISDALL (25 VIII 1878 - 1933). His sister, Eva Therese AUFSEESER (1909 - 5 XII 1940), was also an artist, known for designing greeting cards and notecards. She was married in 1933 to (as his first wife) Gifford Gerald Brereton EDGELOW (c.1909 - 4 XII 1949),
and they had one daughter, Diana Brereton EDGELOW (born c.1938), who was married in 1964 to (as his second wife) Peter Gurney Allen BUCKNALL (7 VI 1926 - 8 X 2017), a descendant of the Pease and Gurney Quaker families.