Rebecca Birley Seixas was the fourth of more than twenty children born to Benjamin Mendes and Zipporah Levy Seixas. Including siblings Moses and Esther, there were sixteen Seixas children who survived infancy—a vast family and among the more prominent in Jewish life in New York. Rebecca’s father was a merchant and a founder of the New York Stock Exchange. Another of the founders, Bernard Hart would become Rebecca’s husband in 1806. They had twelve children, including Emmanuel Bernard Hart, the first Jewish congressman from New York, and Benjamin Seixas Hart.