Mischa's father was the merchant/furrier Siegmund Sender (born on 28 April 1898 in Krakow, Poland), his mother Amalie née Rosenrauch (born on 16 August 1903 in Kolomea, Poland), and his brother Lothar Marcel Leonard (born on 14 August 1929 in Leipzig, Germany). Siegmund died in Nice, France on 10 May 1964, Amelia in Camden, London, UK in October 1979, and Leonard (his preferred name in the UK) in August 1987 in Westminster, London.
Sources: Amsterdam Stadsarchief, Gezinskaarten Amsterdam 1893-1939, archiefnummer 5422, inventarisnummer 1347; England & Wales, National Probate Calendar (Index of Wills and Administrations), 1858-1995, ancestry.com.