Hello Michael,
I"m not sure if you are still around and looking for information on the NZ BELLS. I am descended from William Bell, the mystery man who has been described as the brother of Jonathan Bell, from Foston Farm England. I saw this post some time ago, and it has led to some head scratching because you did not mention William.
In 1851 William and his Sister Ann are recorded as passengers on the Sir George Pollock to Lyttleton. The Lyttelton Times reports that William set himself up in Ferry Road as a farmer and Ann returned to England to report on conditions to her brother Jonathan. I Think they must have meant her Father. When the family emigrated on the Caroline Agnes in 1855 the passenger list shows Jonathan Bell, 54, labourer: Elizabeth Bell, 52, wife: Lucy Bell, 20, daughter: Elizabeth Bell, 18, daughter: and Jonathan Bell, 10, son. It is unlikely that she would be reporting back to a 10 year old boy.
Before 1875 BDM registration was not compulsory, and those that were registered were pretty rudimentary with just the Bride and Grooms names, plus the date of their marriage in many cases.
When William Bell died suddenly in 1884 at Foston Farm, his death was reported in the Lyttelton Times and an autopsy was carried out. This determined that he died of a stroke, and because there was an autopsy his death certificate contained more details that would normally occur in this historical error. So from the death certificate we can see that he was the oldest son of Jonathan Bell and Elizabeth Bell (born Lowe). It also states that he was 59 years old, born at Foston Lincolnshire England, was married to Ann Harvey and they had a daughter, 28, (my ancestor) and a son, 26.
Williams's Death Certificate is 1884004857.
William and Ann are buried in the Church of England Cemetery, Rangiora in unmarked graves on the other side of the path to the monument erected to the early settlers of Rangiora, which is over the graves of his parents.
Hope this helps. Does fill in any of the gaps in your family jigsaw? I am going to add what you said to what I know, and see if it works for William's descendants here.