Don't know how far along you have come with your research since you posted your message, but I think this is the family you were asking about.
IOWA OFFICIAL REGISTER 1933-1934
BIOGRAPHIES OF STATE REPRESENTATIVES
CHARLES J. ZYLSTRA, Hawarden. - Representative from Sioux county, was born in the Netherlands July 31, 1891, and received his education there. In 1909 he arrived in Sioux county, where he has lived since. His interests have been varied, including farming, creamery business, and electrical merchandising and manufacturing. Married in 1912 to Sarah Miedema of Sioux Center and they have one son, Adelbert, and five daughters, Freida, Alvina, Pauline, Bernice, and Marion. Serving first term in the legislature. A democrat.