This would be the Nathaniel baptised at Holbourn
NATHANIEL PYNE
Birth: 03 AUG 1799
Christening: 24 JAN 1800 Saint Andrew, Holborn, London, England
Father: JOHN PYNE
Mother: ELIZABETH
He is the son of Francis John Pyne and his second wife Elizabeth Harvey White and brother of William Pyne the solicitor, who was at one time a friend of Disraelis (I have more notes on this William but they aren’t needed here).
Francis John Pyne was married 3 times
1st (1791) to Priscilla Darnell - 1 daughter Priscilla Pyne (b1792)
2nd to Elizabeth Harvey White, they had John Pyne (b1797)
William Pyne (from Jeremy)
Nathaniel Pyne (b 1799)
Elizabeth Pyne (b1800)
Thomas Pyne (b 1803)
Frederick Pyne (b 1804)
3rd (1809) to Mary Dillman Engleheart - this was the will that Ros found, it names her 4 children including daughter Marianne, - who never married and lived most of her life in Leamington, though in 1901 she is with her sister-in-law Sophia in Kew. Whilst it is just possible that Francis John could also have had Eliza and George, I can’t see that he is likely to have had 2 daughters called Marianne. He died in 1830 and is buried in Bunhill Fields London - there is no will for him in the PCC.