Sam2 – Many families, and perhaps tens or hundreds of thousands of Jews are descended from Rashi, but not everyone in klal Yisroel. None of them is ben achar ben, because he had 3 daughters. I am descended from two of them, Miriam and Yocheved, through a number of lines.
For some more insight into Rashi and Rabbinic lineages I suggest you take a look at the works of Dr. Neil Rosenstein, Rabbi Meir Wunder, and Arthur Kurzweil, among many others.