Jaantje Droomer was a daughter of Nathan Droomer and Mietje van Leeuwen. She married Ruben de Koning in 1891 in Rotterdam. They had at least eight children, among whom Sientje.
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In addition, a Jokos file (number 61432) on this household is at the Amsterdam Municipal Archive. Access is subject to authorization from the Stichting Joods Maatschappelijk Werk.