There is a Public Members Tree on Ancestry - which says the Mother Eleanor died in 1886 - and also has the copy marriage of James' parents. An Alice DENHAM was a witness.

The trees say, George DENHAM brother-in-law aged 19 - was a half brother to Eleanor - but so far they haven't got back further

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? not sure about this 1871 census

1871

James DUNHAM aged 48 (on this census return says he was born in Wales)
Harriet - 49
Edward - 22
Ellen (could be Eleanor) - 15 (born Clerkenwell) as also stated in later census'
George 9