Which woman was the sister of XXX?
Paul Mellon
In 1957, when Fortune prepared its first list of the wealthiest Americans, it estimated that Paul Mellon, his sister Ailsa Mellon-Bruce, and his cousins Sarah Mellon and Richard King Mellon, were all among the richest eight people in the United States, with fortunes of between 400 and 700 million dollars each (around $3,400,000,000 and $5,900,000,000 in today's dollars).
Ailsa Mellon-Bruce