This is a long shot. I looked up Vincent Penz and could not find him on the Ellis Island records site (the free one), but did find a "Vinzenz Penz". As you mentioned his father is listed with an initial in the original ship's manifest, and his sister as "Mona" in Chicago.
The site does not show any "Mona Penz" traveling through Ellis Island or any woman traveling from Raunzertel. However there is an "Anna Penz" traveling to Chicago with her child with an unlisted city of origin. It looks like her daughter's name was Maugarete. There is another relative listed, the one she's going to, maybe Nickolas Pentz, but I'm not sure because of the script.
My great grandmother traveled to the states under her maiden name, it might just be a European thing.
If "Mona" ia "Anna" (sounds similar) it will be a straighter shot. Track her daughter. But if it's another family member, even a distant one, you'll have something. The chances of someone with the "Penz" name going to the same US city if they're not related is pretty slim.
Hope the best for you. Like I said a long shot, but I've had odder.