Thanks again to you all for all the information on this topic. After several hours and lots of paper, I think I have it sorted! Correct me if I'm wrong, but from the information I now have:
Benjamin Fleet (possibly Benjamin Tulfer Fleet??) b. 1796, married Martha Berry/Berry/ Barry b. 1790, in Great Yarmouth on March 11, 1810.
Their daughter Martha Fleet is born June 13, 1810, Great Yarmouth. She seems to be their only child.
Benjamin Fleet dies August 4, 1812 Great Yarmouth.
His wife Martha Fleet (nee Berry/Barry) remarries to Henry Ellis (1790-1843) on May 30, 1815. Unclear as yet when this Martha (b.1790) dies, but she is still alive in 1871, living with her granddaughter Elizabeth in Great Yarmouth, 19, row 120.
So far so good. Now it gets complicated:
The daughter Martha Fleet (b. 1810) seems to have had 4 children:
1) William Benjamin Fleet (base born, 1827, Great Yarmouth). Father unclear. He marries Eliza Sarah Goffin in 1847 (do I have this relationship right??).
2) Robert Nott Fleet (b.1841, Great Yarmouth). Registered as possibly Robert Noll Fleet, but mother Martha in 1851 is living with William Knott, in Great Yarmouth, so paternity may be suggested.
3) Elizabeth Fleet(e) (1844-1933). Probably using the name Fleet still as her mother is unmarried, so she is technically still a Fleet. In 1841 she is probably recorded in Great Yarmouth as Elizabeth Ellis. Her mother Martha (b. 1810) seems to have adopted her stepfather Henry Ellis' name for herself and children. HOWEVER, in 1851 Great Yarmouth, Elizabeth Fleet is now recorded as Elizabeth Knott, presumably assuming the name of the man (William Knott) her mother is living with.
4) Maria Fleet/Nott (b.1846). Paternity may again be suggested by William Knott, and Maria is registered in Yarmouth in 1851 as Maria Knott. This Maria marries Benjamin Moughton in Great Yarmouth in 1869, and using her married name is a witness at her sister Elizabeth's wedding to William James Wells in Great Yarmouth on Dec 22, 1872.
Paternity for all 4 children is only suggested, and I can find no record for Martha Fleet (b. 1810) marrying William Knott/Nott, or indeed anyone else that may give further clues. Birth certificates that I can see only list mother Martha Fleet's name (am I wrong??)
The thing that really confused me was that when Elizabeth Fleet(e) married William James Wells in 1872, she gave her father's name as William Fleete. Initially I thought this was William Benjamin Fleet, but he it seems was her brother (or am I mistaken??). Could it be that Elizabeth Fleet(e) just said her father's name was William (meaning her "stepfather" William Ellis) and it was naturally recorded as William Fleete? Or perhaps she just invented the name to avoid showing unknown paternity?
Huge thanks again to you all for your help with this 'mind bender'. If there is anything else you can add, or I have made some mistakes, please feel free to comment.