In answer to your comments:
You stated: “We should be correct in assuming the parents of John Hastings b.1758 were William and Mary whose death was recorded in the Little Marlow Parish Register in 1791 and 1796 (from the information earlier in this thread). They may or may not be from Cookham originally but by the process of elimination they most likely are.
As you pointed out, just going by the process of elimination, the best candidate for his grandfather is William Hastings baptized 1727 in Hagbourne - Father William, Mother Elizabeth."
I agree with you on that, at the moment my Family Group Sheets for William and Mary and William and Elizabeth have at the top of the page in red print "Possible ancestors" plus an explanatory note.
You: William and Elizabeth Hastings may be far more interesting as they had just 2 born in Hagbourne. William Hastings b. 1726 and William Hastings b. 1727. The one born in 1726 likely died. Then they disappear but a couple of years later a William and Francis Hastings appear in Cookham and have at least 3 children between 1731 and 1736.
Again I agree that this couple William Hastings and his wife Elizabeth Brooks are the most likely couple to be parents of the William Hastings who married Mary Overshott in 1754 at Cookham. That William and Mary were most likely the parents of the John Hastings baptised 1758 at Cookham who married Mary Mitchell in 1789 at Lt Marlow Bucks.
I have a note to the effect that there appears to be no baptism for a John Hastings in the Lt Marlow transcripts around the time to be of an age to marry Mary Mitchell in 1789. Looks like I missed a son named William I only found one child in Hagbourne and that is the William Hasting baptised 1727.
You: Possible scenario where William's first wife Elizabeth passes away after the birth of William b. 1727. He then meets and marries Frances in Cookham bring along his son William b. 1727 which gives a nice explanation as to how William came to live in Cookham and marry Mary and have a son - our John b. 1758.
I haven't yet tried to prove that link, my family group sheet for William and Elizabeth shows only three children for this couple, all three baptised at Cookham:-
William 1757
John 1758
Thomas 1762
I have the following note at the top of the Family Group Sheet for the family of William Hastings and his wife Elizabeth Brooks "N.B. As yet there is no proven link between this family and the John Hastings who married Mary Mitchell nee Clarke at Little Marlow."
Having said there's no proof I think the many uses of the names William, John and Thomas in my wife's Hastings line, although common names they are of some significance.I'd like to make it clear at this point that I'm happy with having any of my theories/comments shot down,