I don't know the origin of the family in Germany. FamilySearch has an early PROELL / BROELL / BROHL family including A. M. Gertrudis, bpt. 17 Mar. 1792, Tiengen A., Waldshut, Baden. Have you checked whether there is any information included in the application for a land patent for Phillip BROHL, Washington Co., WI, Twp. 12 N - 20 E, Section 2, NENE, 46 acres, 1 Sept. 1848?