Hi Squilery
I'm pleased you now have a starting point.

I've struggled to find them in 1881 (not certain if they were already married). I did find this entry which made me wonder as the MIL is called Price.
RG11/5271 F39 P27
16 Shop Row, Llanvihangel Llantarnam, Mon
Thos.
Lloydd 54, Head, Draper, b Llangadock Carmarthen
Sarah 36, Wife, b Builth Brecon
Elizabeth Price 64, MIL, b Llangammch
+ Miriam Nash 19, Servant
In your original post you say you have Ewart Trevor's birth cert. This should show his father's occupation.
Sheila