On my mother's side I am related (in Southern Germany) to the B. family. My grandfather collected data back as far as my 10G-grandfather. I know nothing about his parents, although there is an old family belief that my 10G-grandfather immigrated from Switzerland, where the B. name also occurs. (It is not a particularly common last name, and back to 1589 all members of the B. family in Southern Germany can be traced back to this individual).
I was recently contacted by a Swiss genealogist who shares the B. last name. According to some research that he shared with me, there are three geographic concentrations of the B. name, in Southern Germany, around Zuerich, Switzerland, and in Thurgau, approximately 50 kilometers (30 miles) from Zuerich.
This member of the B. family also indicated that a DNA test had shown that the Zuerich and Thurgau clusters are not blood related.
Would there be any hope of connecting the Southern German cluster into this sample, to settle whether or not there is a relationship between my cluster and one of the other two?
As I said, I assume that one must go back at least ten generations, and I assume that the DNA has been pretty well shaken up, mixed and diluted in the meantime.
Is there any hope of getting meaningful results out of such a test?
How large a sample might be needed?
How diverse would it have to be, that is, how far back along my cluster of the family would I have to go in order to have a hope of definitive results?