Thanks Mohnbauer for all your help. My major problem is that I don't have surnames for some of these people. If I can find out my grandmother's(Katharina Kerstein) maiden name that might be a great help. The Plesin brothers that came to the US had no children and my immediate relatives have no information. I did send an e-mail to the diocese of Trieste, who I was told had records for parishes in my area of interest, but have not had any response yet. Most of my information has come from postmarks on postcards sent to my grandmother, from Villach, Weissenfels/Fusine ValRomano, and a passport from Ratschach (Ratece).
I may be planning a trip to these areas next year and would like to have some idea what genealogical information I'm looking for while I'm there aside from enjoying the beautiful scenery!