I realized that rushing I had misspoken before. I think that the most likely thing here is that Julia's mother Caroline was a sister of Frederick Grapengieser, though his name does not match with Fritz. (middle names are given as different by his family member.)
The marriage of Caroline Grapengieser to Johann Krull in Wauwatosa is the most intriguing to me. Perhaps a family member would know where that took place, or have the name of a pastor who married them. I might then be able to find that church record and move forward to trace the relationship between my Ziemers and the Grapengiesers.
Let me know if anything shows up in Milwaukee.
Warm regards,
Penny