Willem Schaap was a son of Abraham Schaap and Roosje Heilbron. He married 5 December 1906 in Amsterdam to Elisabeth Groen, daughter of Juda Groen and Vrouwtje Haringman. The couple had three children: Abraham, Juda and Philip.
A sister of Willem Schaap was Marianna Schaap, spouse of Benjamin Visjage…
In addition, a Jokos file (number 12559) on this family is at the Amsterdam Municipal Archive. Access is subject to authorization from the Stichting Joods Maatschappelijk Werk.