have you both tried Family Search?
There is a Joel Rowsell on the IGI, born 2 September 1822 and baptised 4 October 1822 at St Andrew's Enfield, Middlesex. His parents were William and Susannah.
There are 4 siblings baptised at the same church:
James Meade ROWSELL, bap 24 November 1816
Anne Amey ROWSELL, bap 8 September 1819
William ROWSELL, bap 8 Feb 1826
George ROWSELL, bap 23 September 1829
Of course, there is no guarantee that this family has anything to do with the Joel Rowsell that you are searching for. However, the location seems about right, particularly considering Emily's birth registration in late 1859 in Edmonton.
However, Edmonton district does not take in the Strand area where Joel the bookseller had his business.
Are you sure that you are chasing the same man and the right Joel Rowsell?
Unfortunately I have not been able to locate a marriage for Joel Rowsell using FreeBMD, except for one in June qtr 1839, registered in Medway, vol.5, p.396. The bride would have been either: Catherine REID or Charlotte SCEARS.
However, noting that Joel Rowsell the bookseller may have had a lifespan of 1806-1886 (though not sure of the evidence for this), going back to FamilySearch there is an earlier Joel Rowsell, apparently born 5 Jan 1797, but baptised in January 1802 at St Mary le Bone, Middlesex, son of Aaron and Ann Rowsell. I can't find any other children with the same parents.
Of interest are the Wills in the National Archives' Documents on Line:
http://www.nationalarchives.gov.uk/documentsonline/ A Joel Rowsell, nurseryman of Enfield has a probate 23 Jan 1843.
A published obituary in The Athenaeum, suggests that Joel Rowsell went to sea in his early years, but after 3 shipwrecks turned, in 1828, to bookselling. Firstly as assistant to Mr Ward of Holborn, then to Mr Robinson of Brownlow Street. Established his own business in 1856 in King William Street. Retired in 1882 and sold all his stock. Died 24th June 1886, age 80 and buried at Highgate cemetery.
Without a definite birth record for him, I would take that nice round figure of 80 years at death with a little scepticism until proved - the person notifying his death may not have been entirely sure of Joel's age.
Happy hunting.