Only because you didn't list these sources for additional connections or hints, I'm suggesting them here:
baptism sponsors? the other marriage witnesses? other immigration witnesses? for any of these Fischer folks. Did the ex-Mrs. Lorenz Fischer list her immigration year in the 1900 census (in case they arrived together unmarried.) Any unmarked, anonymous grave in a family plot with those 3 young Fischers or the other Fischers? The Lorenz names in my tree are listed as Laurence or Lawrence Lawrenz in 19th C. records recorded by local non-German clerks.
The German newspapers regularly report the finding of unidentified persons pulled from the river or found elsewhere with detailed descriptions of clothes and contents of pockets provided by the Coroner's office. These articles are followed up until the unknown is ID'd, but sometimes reported as being buried at the County Farm as unknown.
The German papers themselves record the difficulty when reading German handwriting on envelopes; the German letter lists in 1865 include an entry: Johann Tischer (Fischer), letter postmarked from Roebel. Some florid German handwriting on the State of Wisconsin's vital records for one period have a capital F and T that are identical except for the almost invisible cross-hatch on the vertical trunk of the letter denoting F.