The best match I can find for Sarah Pike is an Ann Sarah Pike baptised in the West Drayton parish (now part of the London Borough of Hillingdon) in Dec 1812 (I'm basing this on the fact that her birthplace was listed as "London" on the 1851 & 1861 Censuses). Apparently she was born on Nov 13th 1812 and was the daughter of Sarah and James Pike. The good news is that it looks like she might have had a brother named Richard who was born to parents of the same names and baptised in Monkton, Devon in 1813... although why the parents were in West London in 1812 and then rural Devon the following year

James' occupation is given as labourer, so maybe the family travelled to Devon to work on the land during the summer months?
(There's also a Sarah Pike who was baptised in Feb 1812 at St. Mary's in Earl Stonham, Suffolk. She was the daughter of Sarah and George Pike, but I can only link a Richard born in 1830 to them, so too young to have witnessed the certificate in 1836.)
Certainly feels like Charles' time line is now:
- 1791: Charles born in Dedham
- 1823: daughter Susannah born in Dedham
- 1823/4: moves to Stratford with his wife and 1st daughter Susannah
- 1824: daughter Sarah born in Stratford
- 1828: son Joseph is born in Stratford
- first wife dies sometime before 1836
- 1836: Charles marries Sarah Pike in Bermondsey (only a few miles from Stratford)
- 1838-1844: Charles' other 3 children born to Sarah in Stratford
- 1851 Census: Charles is working as a fishmonger in Stratford
- 1858: Charles dies in Stratford
- 1861: Widow Sarah continues running the fishmongery and greengrocery business in Stratford with sons Charles & Enoch
I can't find a death in Stratford that would fit Charles' first wife, but there is a Sarah Hitchcock whose death was registered back in Dedham in 1832 aged 69. Assuming the first wife came from Dedham, maybe she wanted to be buried back there?
I've got nothing definite for Sarah Pike's death, other than a Sarah Hitchcock who died aged 57 and whose death was registered in Dunmow, Essex, in early 1867.