This won't solve the problem of the Williams, but it'll give background data. Have you done a Google Search? Try
"Skiff(e) Family of Martha's Vineyard"
John, Jr., #131, b. 14 Jan. 1762, MA [from pension record]; m. 8 Oct. 1780, Mary MAKEPEACE. Their children are listed as Samuel, James, William, Benjamin, Charity, Hannah, Abigail, & Bathsheba, but I don't know the source of the information on the children. John, Sr., b. ca. 1728, m2. 1781, & had a William, b. 15 Apr. 1785, Chilmark. Have you differentiated the two Williams?