hmmm, I have 8 children for John but I don't think they were all Margaret's - I have her dob as c1663, and the youngest John Sankey child I have is Mary Sankey - born 1675, plus an undated Elizabeth?
But I'm also not sure that John had any earlier wife?
Margaret was supposedly the wife of the farmer where John worked, and he married her when the farmer died - which would seem to make Margaret the one with an earlier marriage!