Hello Bel, hope you have had a nice Easter holiday. I do not have access to the 1871 Census however I have the 1841/51 & 61 and uk 1881.
I searched the 1841 disk but no luck, even looked under variants such as Coles etc. There was a N Cowles but the birth year was way out.
Same with the 1861 ~ no entries listed for the name at all.
With 1851 we have a hit!  

Here are all the entries:
2461 531 013  LLAMPHA                COW JOHN                   VR U  27    SCT -                           
2455 122 173  6 EAST TERRACE         COWLES FLORENCE            WI M  45    MON USK                         
2455 122 173  6 EAST TERRACE         COWLES JOHN M.J.           SO -   1    GLA CARDIFF                     
2455 122 173  6 EAST TERRACE         COWLES WILLIAM             HD M  45    MON MATHERN                     
& here is the specific entry:
2455 1851 CENSUS OF CARDIFF (NORTH-EAST). REF.H.O.107/2455, E.D.4B.                                                                  
Piece: 2455      Folio: 122     Schedule: 173
Address: 6 EAST TERRACE         
COWLES WILLIAM             HD M  45   ACCOUNTANT                
                                      MON MATHERN                      (c1806)
COWLES FLORENCE            WI M  45   -                         
                                      MON USK                          (c1806)
COWLES JOHN M.J.           SO -   1   -                         
                                      GLA CARDIFF                      (c1850)
REGAN CATHERINE            SV U  16   HOUSE SERVANT             
                                      IRL -                            (c1835)
It could be they moved between 1851 & 1861, or they are enumerated under the wrong spelling that I have not searched for.
With regards to the unusual names, people I have found in my research named their children after a family member (Grandfather of either Maternal or Paternal family, or a brother etc) sometimes after a deceased family member e.g: child in the family.
The names do seem unusual, Milner Jenkins, could be after the Mothers family (maternal and Paternal names) keep all the names in mind when researching, sometimes things you find initally will fit in nicely much later on. I say this especially as you are unaware as to Florence Cowles maiden name at the moment. 
Give me a few days (the children are home from school so I have been a little short of time for undisturbed access to the internet!!!!) I will see if I can help you...no promises but you never know I may turn up something for you.
If you have any other information which you think may help let me know.
I will post here to let you know either way.
Take care & happy researching 
You have picked a very addictive hobby! 

Kindest Regards Jen  
