I'am from Aachen Germany. My father Peter Bau and his family come from Stolberg, Germany, which is very close to Aachen. His father's name (my grandfather) was Heinrich Ignatz Bau. His father's name was (again) Peter. His father's name was Wilhelm Bau - so that is my great-great-grandfather. Supposingly he had like 12 siblings, but 2 died when they were young. So that should have yielded plenty of offspring. Thus most Bau's living in Germany are probably related to each other, as there are not that many - just looking in the phonebook .... .
Maybe that helped someone. If anybody feels like there is a link to my ancestors, feel free to contact me. By the way: my grandfather always thought that the Bau family derived from Belgium or France. However he might have been wrong - I don't know ....