I agree that William was very likely the son of Isaac Bush. A new DNA submission from a proven descendant of James Bush (reputed son of Isaac and brother of William) confirms that James Bush was a direct desc. of Abraham Bush.
Would you mind sending me a transcript or detailed abstract of that deed you mentioned for William claiming he was from St. Mary's Wh. Chapel Parish??? IT would really help!
WE are trying to confirm that Isaac Bush did have these 2 sons William and James with certainty.