We may be related but it is not yet clear. Thomas Twitty, the first recorded Twitty in the US, had two sons, John and Captain Thomas. I've followed the links and find that Captain William Twitty appears in Rutherford Co. N.C. about the same time as Thomas Twitty's grandchildren were born but I see no link of Capt. William with Thomas's family.
Captain Willian Twitty was indeed killed by the Indians as noted by Felix Walker, one of the men with him: "We placed ourselves under the care and direction of Capt. William Twitty, an acitve and enterprising woodsman, of good original mind and great benevolence, and although a light habited man, in strength and agility of bodily powers was not surpassed by any of his day and time, well calculated for the enterprise." An Indian attack in Kentucky fatally wounded Capt. Twitty and killed his slave, Sam, outright. A small fort was erected on the spot and named Twitty's Fort or Small Fort.
Capt. William Twitty married Susannah Bellars and amoung their eight children was Bellariah Twitty who married Joseph Green and they had nine children, one of which was Eliza Green and she married Allen McFadden. It is from this link with Green that the Twittys and McFaddens are related.