Cosman Troostwijk and his wife had four children. One of the daughters was Hendrina Julia Troostwijk. She was married to Albertus Julius (also known as Albert Jules) van Gelder.
Cosman Troostwijk stored a case with silverware and jewellery with depositors in Leeuwarden. The case was located by the Nazi authorities and seized.
The archive of the Stichting Sieraden-Comité contains among other things a list of stolen items of jewellery, a declaration under oath and a statement of the right to inheritance from 1946.
NIOD, Records Stichting Sieraden-Comité, box 7HF, file 91
In addition, a Jokos file (number 9926) on this family is at the Amsterdam Municipal Archive. Access is subject to authorization from the Stichting Joods Maatschappelijk Werk.