I have Victor's ancestors going back to the 16th century, but unfortunately no siblings listed. My source (not entirely sure who -- my late aunt had a lot to do in this, but there may have been someone else, possibly a correspondent) was more interested in Theresa's family, the Oechslis.
In any case, Victor's father was Jeremias (1804-1860), grandfather Joseph Meinrad. Does that tie with anything you know of your great-grandfather?
Let me know -- I have some stuff I can send you, including a photo of Victor and Theresa and their daughters.