Hi again,
I think the family you have from 1881 is the same one I found in 1861/71 since I can only find one Hannah GRIFFITHS of about the right age in both 1871 and 1881.
Here are the details of the entries I found in 1861 & 1871:
1861 Census Bettws (RG9/4133 Folio 27 Page 12)Address: LynyCoed Cottage
Rees GRIFFITHS, Head, 44, Blacksmith, b. Llandilo Parish Carmarthenshire

Sussanna ditto, Wife, 42, ditto Wife, b. Bettws ditto
William ditto, Son, 15, Blacksmith. b. ditto dittoJeremiah ditto, Son, 10, b. ditto ditto
Ann ditto, Dau, 8, b. ditto ditto
Isaac ditto, Son, 3, b. ditto ditto
1871 Census Bettws (RG10/5412 Folio 8 Page 7)Address: Oddfellow's Row
William GRIFFITHS, Head, 29, Blacksmith, b. Bettws, Glamorganshire
Hannah GRIFFITHS, Wife, 26, Blacksmith's Wife, b. ditto}
Mary Ann GRIFFITHS, Dau, 6, b. ditto
Elizabeth GRIFFITHS, Dau, 3, b. ditto
and next door at The Oddfellow's Arms:
Rees GRIFFITHS, Head, Widr., 61, Publican, b. Bettws, Glamorganshire
Elizabeth GRIFFITHS, Dau, Unm, 23, b. ditto
Helen GRIFFITHS, Grandau, 3, b. ditto
There are some inconsistencies in the ages between the different censuses but this is not that unusual. I definitely think it would be worthwhile looking through the marriage indexes, working back from 1865 to see if you can find William GRIFFITHS on the same page as a Hannah with one of the surnames from my previous post.
Regards,
Al