Roots again

We caught the end of a television programme which traced the family history of Fiona Bruce, a tv newsreader. In the programme she visited the local history centre in Brighton, a resource I hadn't known existed. They seem to have a great number of old directories, parish records etc which are available for family historians for research. I really must pay a visit to see if they can shed any light on the mystery of Sheila's grandparents. What I have at present is as follows.

1879 - grandmother Constance Emma Brown born near Newhaven.
1881 census - family now living in Bevendean.
1891 census - Constance no longer with the family and I have been unable to trace her in the census.
1901 census - Unable to trace Constance in the census, but
1901 census - Constance A Brown, 21, a fishmonger's manager, was living in Brighton, with the Paris family. Could this be her? Edward Paris was a cab driver.
1904 - Mother (Margaret Eva) born in Brighton, name registered as Margaret Eva Brown, father William Brown, mother Constance Emma Brown, formerly Brown. William Brown was a cab proprietor.
1904 - Margaret Eva Brown baptised in Streatham, a London suburb 40 miles or more from Brighton, but as Margaret Eva Jones.
1911 census - Albert Jones, Constance Jones (grandparents) and Margaret Jones (mother) living at a different address in Brighton. Albert Jones (a taxi cab driver) & Constance Jones supposed to have been married 9 years, but unable to find any trace of marriage. Albert Jones born about 1877 in Norwich. Margaret Jones stated as born in Philadelphia, USA!
1911 - Ivy Vera Brown born in Brighton. Father registered as William Brown, a taxi driver, mother Constance Emma Brown, formerly Brown.
1912 - Lillie (sic) Jones born in Brighton. Father shown as Albert Jones, a taxi driver, mother Constance Emma Jones, formerly Brown.
1913 - Lily Jones dies in Brighton. Daughter of Albert Jones, a taxi driver. Informant C E Jones, mother.

Unfortunately, William Brown was a very common name in Sussex at that time, so there is no hope of tracing his birth with any confidence, and I have been unable to trace any record of a marriage of Constance Emma Brown. But apart from that, there are a couple of mysteries. Why was Margaret baptised in Streatham when, as far as we can tell, the family had no connection with that area? Why did William Brown chop and change his name between Brown and Albert Jones? Why did Albert Jones state in the 1911 census that Margaret was born in Philadelphia? We shall probably never find the answers to these questions, but I must try to do so because both Sheila and I are extremely curious.

I have changed the names in this post in the interest of security,
as one so often needs to give one's mother's maiden name
in answer to a security question.