Ok - here's where my info differs from yours.
Thomas Venable I - died 1731 in Philadelphia. His second wife was named Rebecca and she died 1784 and is buried beside her husband at Christ Church in Philadelphia. I think his first wife was Elizabeth Lee.
Thomas Venable II born about 1709 married Sarah Wallis in 1729. He died 1778.
Thomas Venable III born 1731 (same year his grandfather died) and married Esther Borradail 1756. He died in 1774.
They are the parents of Arthur born 1757.
Thomas Venable IV born to Thomas III in 1761 and died 1763.
Thomas Venable V also born to Thomas III in 1771.
So my question is this: Is the Thomas Venable I listed above related to this line or not? I noticed he was not included in the info you listed. Please advise.