Isaak Wohlgemuth on 1893 Elbing list
Virtual Shtetl has lists of Jewish Households and Individuals in Elbing for a few random years in the 1890s and 1900s. Following is the list for 1893, where we find Isaac Wohlgemuth listed as "Kaufmann" (merchant) along with two other Wohlemuths, Witwe and Heinrich. (I'm not sure, but you may need to be logged in to the site to access the page.)
There are also lists for 1900-1 and 1905-6. On the 1900 list the same three Wohlgemuths are listed using first initials only (Isaac is identified as "J. Wohlgemuth".) However, in 1905 there are no Wohlgemuths listed.
This is great because it definitively places our ancestor as a merchant in Elbing between the years 1893 and 1901. We also know that Elly was born in Elbing in 1901. It also shows that Isaak no longer resided in Elbing by 1905, which is consistent with the fact that Hilda was born somewhere else (Danzig) in 1906. Whether they remained settled in Danzig or perhaps relocated again (to Konigsberg) is to be determined.
The two new Wohlgemuth names, Witwe and Heinrich, are new to us. The name we might have expected to see—Leopold, Isaac's father—is not listed. Is he perhaps deceased by 1893 or else still in Stargard? If so, are Witwe and Heinrich brothers of Isaac? They could also be cousins or similar relation. ( Elbing is only about 30 miles from Stargard although it was across the river in East Prussia.) It is interesting that Witwe and Heinrich are also absent from the 1905 Elbing list, suggesting that they all may have moved together.
Welcome home, Jo. This is the second time your traveling investigations have resulted in fantastic discoveries.