John Kerry is also from the Kohn family.
Here is some members of the Winthrop family:
http://www.nndb.com/group/473/000127092/
The Kahn family is listed at #30, they are of Kuhn, Loeb and Co, but I don't see his name listed there. Wouldn't doubt it though. Here's a complete listing from that book, America's 60 families: http://www.nndb.com/lists/439/000127058/
There is a distinct resemblance between John Kerry and Sally Kohn.