>>>Still, it's a little funky how just 4 people left so many descendants. . . . what happened to the other descendants of all the other Jewish women living in Franco-Germany about 1000 years ago?
We don't each descend from one person. We have many ancestors - think your grandparents on both sides, their parents and grandparents, etc. Over 1,000 years there are many opportunities for gene lines to overlap. Given any two people who share the same culture and origins, odds are probably 10-1 that they'll find a common ancestor somewhere up the line.