Hi again,
I think I have just found David and Elizabeth in the 1891 census for you.
The problem is there are an awful lot of David Jones' born Cardiff in the time period 1865 (1863-1867) but this one is with his wife Elizabeth A. born Merthyr.
here are the details, but I have not checked all the other David Jones'
David Jones, Lodger, M, (married) 26, Labourer, Employed, b Cardiff Glamorgan
Elizabeth A Jones, Lodger, M, 23, b Merthyr,
Address: 5 Amos Hill, Civil Parish Llantrisant, Glamorgan.
They are lodging with the Lynch family.
John Lynch, Head, M, 50, Collier, b Ireland Cork.
RG12/4418 folio 81, p 6
hope that helps, now you know they were married (probably) before 1891 which will help in the search
Newbie