Sorry, I was trying to work back to double check your information but to be honest I found your initial post difficult to read as it was one very long paragraph so did not proceed with it as far as I would have liked.
As you have now confirmed that you have the marriage hopefully we can go back further with this.
This is where I get suspicious Robert Mason has 9 children. One of these was Robert Mason 1757-1849 who went to America and fought for the rebels earning the nickname 'The Patriot'. American contacts and trees I have seen have his mother as Elizabeth Dudley, I cannot find a marriage of a Robert Mason to a Dudley. I have a marriage 1749 to Elizabeth Lee.
Where the Americans get Elizabeth Dudley from I don't know. Maybe some clue in Ann Dudley Mason.
Baptised St Mary, Whitechapel - parents Robert & Elizabeth
William Mason 15 Dec 1750 - Mill Yard
Elizabeth Mason 25 Oct 1752 - Mill Yard (not on your list)
Sarah Mason 14 Feb 1755 - Rosemary Lane
Robert Mason 24 Apr 1757 - Rosemary Lane
Elizabeth Mason 22 Jul 1759 - Whites Yard
John Mason 29 Mar 1761 - White's Yard
Ann Dudley Mason 5 Dec 1762 - Whites Yard
Charlotte Mason 3 Jul 1765 - White's Yard
James Mason 4 Sep 1767 - Rosemary Lane
Charles Mason 25 Dec 1770 - Whites Yard.
Could it be that there are two different families here ? It is definitely worth considering