I'm wondering if off your research of the Siemer family may have included Gerd or Elisabeth Siemer? I have traced back and can find nothing else on this family.
Here is what I have:
Wilhelm Heinrich Feuss was born at Ehrling/Rehden 19 May 1820 to Wilhelm Feuss, a tenant and Elisabeth Siemer, wedding at Jacobidrebber 24 Oct. 1800
Wilhelm Feuss was born at Wagenfeld 24th of Nov. 1777. Elisabeth Siemer was a daughter of Gerd Henrich Siemer.
Elisabeth would be my 4g grandmother.