Please forgive me if I am doing this in a clumsy way. I am new to RootsChat.
In the 1990s I corresponded with a Sinnock in the USA who was doing a lot of Sinnock genealogy. He sent me a "hard copy" of his tree. I know that he did a lot of research, but he also received sub-trees (if you will) from other Sinnock descendants and added them into his tree if there was a common ancestor. I doubt that he had time to validate all his entries before I lost contact with him in the late 1990s. So I offer the following from his tree because a lot of it matches the information in this thread, but with the caveat that I do not know for certain how much of it is accurate. Nevertheless, even if it has some errors, it may provide some ideas for more searches. It also suggests to me a possibility as to why Mary Ann Sinnock has been a bit elusive: there are two of them. OK, so only one is the daughter of Thomas and Jane.
Thomas Sinnock b. May 30,1757 Hailsham, East Sussex
+ Jane Thatcher b ABT 1775 Sussex or Kent d 1820 Hastings, East Sussex
Elizabeth Sinnock b. October 04,1797 Hastings
Jane Sinnock b. January 18, 1801 Hastings
Mary Ann Sinnock b. June 20, 1804 Hastings
Thomas Sinnock b. 1806 Hastings d. Aft 1861
+ Ann ? B. ABT 1804 Winchelsea, East Sussex
James Thomas Sinnock b. June 18, 1833 Hastings d 1910 Hastings
Mary Ann Sinnock b. February 04,1837 Hastings
Elias Sinnock b. January 11, 1839 Hastings d. 1864 Lost at sea.
Jane Sinnock b. ABT 1842 Beckley, East Sussex
Robert Sinnock b ABT 1845 Beckley
In addition to this information, Thomas ( b 1757) is listed as the son of
James Sinnock b. July 15, 1732 Westham, East Sussex d. January 10, 1813 Hailsham
+ Sarah Marshall b October 07,1733 Hailsham d. November 13,1811 Hailsham
Thomas Sinnock b. May 30,1757 Hailsham [see above]
James Sinnock b. August 11 1758 Hailsham d. November 1839
+ Elizabeth Weller b. June 28, 1759 Hailsham d. February 1830
John Sinnock b. July 04, 1764 Hailsham
Elizabeth Sinnock b. March 23 1766 Hailsham
Samuel Sinnock b. October 28, 1770 Hailsham
Henry Sinnock b. September 13, 1778 Hailsham
+ Mary Wood b. ABT 1780 Kent
... And this is my tie-in. Henry and Mary are my ggg Parents.
John