Collins help please

[kiterunner]

I'm trying to work out whether a certain couple are mine or not.

This is definitely my relly Henry Farmer on the censuses:

1871:
315 Ebury St., Belgrave, London
Mary Farmer Head Wid 54 Somerset Bath
Hy Do Son Widr 33 Omnibus Conductor Bath
Louisa M Do Gd Daur 2 Middlesex
Rhoda Do Gd Daur 1 Middlesex
Geo S Smith Boarder Unm 44 Banker's Clerk Windsor

1881 census:
33 Westmoreland St., St George Hanover Square, London
Henry Farmer Head Mar 41 Bath Attendant Bath
Elizabeth Farmer Wife Mar 29 Seamstress Hampshire Andover

1891 census:
177 Vauxhall Bridge Road, Westminster
Henry Farmer M 51 Money-taker (shop) Bath
Elizabeth A Do Wife M 39 Upholsterer Hants Andover
Louisa M Do Daur S 22 Seamstress London Pimlico

I haven't been able to find Henry, Elizabeth or Louisa in 1901. Rhoda is with her aunt Kezia Russell in Somerset. There is a possible death for Henry in 1897 in Islington.

I had noted down a likely marriage for Henry and Elizabeth but now the marriage certificate is up on ancestry I can't work out whether it is them or not!
St Mary Lambeth July 13 1879
Henry Farmer age 40, widower, Wood Carver, Carlisle St., father William Charles Farmer, artist.
Elizabeth Ann Collins, 27, spinster, Carlisle St., father James Collins decd, Musician.
Witnesses Thos Nettlefold and Ellen Roberts. I've seen the name Ellen Roberts on St Mary Lambeth marriages before so I think we can ignore her.

My Henry's father was plain William Farmer, a labourer, as far as I know, and I had assumed he died before 1851 as Mary is a widow on the 1851 census. Henry's occupation varies from census to census but he was an Engraver on Wood in 1851. There is an Elizabeth Ann Collins birth registered in Andover in Jun 1852 but I haven't managed to find her in 1861 or 1871 to see if her father was James.

Help please!