Auctioneers Bonhams will sell the paintings on November 13 at New Bond Street, London.
The paintings are by Jacek Malczewski (Polish, 1854-1929), one of the most famous painters of Polish symbolism and are estimated respectively at £10,000-15,000 and £2,000-3,000.
The Radziwill family has been the most powerful aristocratic family in Poland for 500 years, creating and preserving enormous wealth and influence.
The family was ennobled by the Holy Roman Emperor and over the centuries has produced many exceptional politicians, entrepreneurs and military commanders who have helped to shape Poland's history.
Outside of Poland, the Radziwill family is probably most famous for its connection to Jackie Kennedy Onassis, America's most renowned First Lady.
Jackie's younger sister, Lee Radziwill, entered the family in 1959 when she married Prince Stanislaw Radziwill.
The couple had two children, Anthony and Anna, although they divorced in 1974.
Anthony died in 1999 aged 40, just two weeks after the death of his cousin John F. Kennedy and his wife, Carolyn, in a plane crash in Massachusetts.
The portraits are the property of the late Prince Jerzy Mikolaj Radziwill, who died earlier this year.
The first is an oil painting of Witold Hausner (1852-1925) and the other is a watercolour of his wife, the Marchese Guilia Asinari Di Bernezzo.
The Hausners and the Radziwills were supposed to be good friends and it is believed that the paintings passed into the Radziwill family through this friendship.
Text and image by 999Network