My records only begin with Simon Foscue, born about 1734.I do not have a record of his parents or siblings.
I did see on a Foscue Family Tree: Simon Foscue, born abt. 1734, married Sarah Sanderson, daughter of Benjamin Sanderson on Mar 19 1759 in NC. I don't know if this is correct as my records show that Simon married Sarah A Brockett, born about 1739, in 1759.
As you mention a 1751 will, I suppose you are referring to an earlier Simon.
I have recently realized that the handwritten record that I have that was compiled down to 1911 was written by a relative that was living in Salt Lake City at that time.I believe that she got her information at the LDS center there, and it was not handed down to her from her relatives.