Johan de Witt
Bicker was married to Agneta de Graeff van Polsbroek, a sister of Cornelis de Graeff. Three daughters were born from this marriage: Geertrui, Wendela and Jacoba Bicker. Geertruid married Jean Deutz, Wendela married Johan de Witt and Jacoba was the wife of her cousin Pieter de Graeff. De Bickers were part of the "staatsgezinde partij" (the pro-republican party) and opponents of the stadtholders, who belonged to the House of Orange-Nassau. Jan Bickers son in law, the influential Grand Pensionary Johan de Witt practically controlled the Republic during the First Stadtholderless Period in 1650–1672. Several ownerships of Jan Bicker, amongst which the countryhouse 'De Eult' in Baarn, eventually fell into the hands of the stadtholders.