I do not think there is any doubt but that King was brought up by his Uncle Robert at the Lamb Hotel in Ely. My main reason for saying that was that he was brought up as "King" not Billett, Robert having a son called Billett and the one was not to be confused with the other.
King Genn married Mary Wilson Talbot (a Cambridge girl - dtr of William and Ann) at St Giles London in 1835, Mary was 20. They settled in Cambridge.
King was (somewhat amazingly given his ancestry in the 17th century) first a tailor, robemaker and hatter and had a shop in Rose Crescent, still a popular shopping street in Cambridge. My guess from his being a robemaker was that he catered for the university set. I know that he put himself about in the 1830s, and was a member of the Cambridge Garrick Club, the cousin of the London theatrical club of that name.
Rose Crescent
The family briefly went to Willow Walk but by 1851 were in Brunswick Place, King having pulled things together and established himself as an accountant.
By 1861 the family were in Nelson Place, and things took a turn for the worse again in 1863, the Cambridge Independent Press reporting a court case (also reported in the Cambridgeshire Archives) where it seems King was behind on the rent and the family were evicted from their house in Nelson Place. He was in a bit of a state at this time and I know was a Sexton at St Edwards Church and was dismissed from his post in 1866 because he was not carrying out his duties satisfactorily (Cambs Archives)
St Edward
King stayed as an accountant the rest of his life. They continued to move around, likely renting, being at 29 Bullen Place in 1871 and 16 Union Road Cambridge in 1879 where Mary sadly died aged 63.
While still at Union Road in 1881, King shortly afterwards moved to Wandsworth in London, perhaps to be nearer to one of the children. He died there in 1886 aged 81. He and Mary are both buried with a gravestone in Mill Road Cemetery Cambridge.
King and Mary had nine children:
Mary Ann - died unmarried in 1879
Annette Talbot - married Jesse Ross in 1862 - they went to London
and there are descendants
William Henry - he married Emily Sarah Styles (a Cambridge girl) in Richmond in Surrey in 1876. They had only the one child, Violet Birdie, who died unmarried. Exceptionally for this study, William was a Landscape Artist - he obviously made a living at it but no works are known.
In 1863 he was a Pupil/Teacher at the Cambridge School of Art which was founded by John Ruskin in 1858 and is still going strong below
Sadly William died prematurely on Christmas Day 1891 aged 50. He is buried with his parents. Emily ran a lodging house thereafter, never remarried and died in 1933 buried with her husband and in laws in Mill Road Cemetery Cambridge.
Susannah King - married Stephen Adams in 1900
George Charles - married Elizabeth Smith Ablett in Chelsea in 1874. He was a clerk and they lived in Surrey. It is unclear whether there were issue. George died prematurely in 1887 aged 42. Elizabeth remarried David Gill in Chelsea in 1892.
Emily - she lived in Surrey with her sister Susannah for a time, was later a Cook and never married, working at one point for a well known golf club. She died in 1918 aged 71
Martha Charlotte - died unmarried with her Dad in Wandsworth in 1882 aged 32.
Florence Kate - married Stephen Nicklen in Wandsworth in 1880
John James - died in infancy
Acknowledgement - I am indebted to the Friends of Mill Road Cemetery, Cambridge, for some of the information that appears here