Hi Melanie,
1. Your family is mostly probably from Karlsruhe, Stavropol, Russia. See:
http://www.grhs.org/villages/caucasus/karlsurhe_ncaucasus.html This is located in present day Georgia, almost directly below Moscow. Be careful as there are several Karlsruhes including one in present day Ukraine - which is not the correct one.
There were a number of families from this area that emigrated to Rosthern. I believe with a large enough tree that we are all related.
2. Many of the Karlsruhe settlers were first located in a Volga Colony. See
http://wc.rootsweb.ancestry.com/cgi-bin/igm.cgi?op=SHOW&db=volga%5Fstier&recno=16415and you will find a number of Gerlachs. My great-great grandfather is on the list of Volga settlers, but sometime the family moved on to Karlsruhe, as that is where the family lived before they emigrated to Canada.
3. Unfortunately, the 1897 Russian census was destroyed in a fire - which wiped out at least a generation of records for the people we would like to put in our trees. For example, my great-great grandfather, Conrad TRIOL is on the Volga database, but my great-grandmother Katherina Elizabeth was too young to be found, as was my grandmother, Maria Katherina HELMUTH aka KNIPPEL. So you may gain info from the Volga records, but then have to jump to the Canadian census.
4. You will find that most of the Russian Germans were married more than once. Such was the mortality rate at that time. I, too, suffer from the problem of blended marriages and multiple spouses.
5. Your family is mentioned in Old and New Furrows: the story of Rosthern, which can be read online at our roots.ca; pg 573-575 - if you have not seen that. Reading through this confirms your connection to the Volga village of Warenburg.
6. Do not worry about the spelling of the names too much - you should be looking for Gerlach - the others are simply phonetic guesses. The Swabisch dialect used by this people seems to have been difficult to understand.
If I can be of further help, please let me know.
Laurie