some additonal information:
1. Here you will find some resources regarding confirmed names and their relation to a spesific settlement for the name "Schwartz"https://www.volgagermans.org/w...s/schwartz
2. The same as above for the name "Fuchs"
(scroll down for the end of the list, many entries for this name !)https://www.volgagermans.org/w...surnames/f
These links will also gives you a hint where these people might come from in Germany.
On the top menue you will find a link for "Resources", following this you will find a list of "revision list" means listing of people in a specific place at a specific time.
They also mention where to find these lists, some are only available as a printed book, some online at www.familysearch.org
The 10th revision took place in 1857 maybe its possible to find at least the family (mother and/or father) of the two persons in question.
3. The "Amburger Database" can be found here:https://amburger.ios-regensburg.de/
You can enter a name and check the results for any connection to your persons.
The contents is build up of people living in Russia before the Russian Revolution by extracting many different sources.
Just an impression from my personal research, it looks like its more easiy to find people in official jobs (military or senior officals etc.)
This database can give you better hints if you already have some knowledge about firstname/lastname and places of living...........
Question: Are there any documents in Argentina about the incoming immigrants ? Maybe you should check this first in order to get a smaller timeframe for further researches.......just an idea.