Dusty, I called at the Archives today and looked at the Burial Index for St Hilary's Church Llanrhos. These Burial Indexes list all the graves with inscriptions on them and the people are also listed alphabetically so it's easy to trace.
However there is no Huw Davies or Mary Jane Davies listed there. I tried other variants like Hugh and Mary but again they are not listed.
Just in case I tried St Tudno's, Llangystennin and Glanwydden but again their names are not listed.
This does not mean that they are not buried there but that a headstone with an inscription is not listed in the usual place.
I checked the Street Indexes for 1911,1914 and 1929 but they are not listed at Pen Y Groesffordd either.
I looked on Ancestry but because your information is vague I couldn't trace them. I tried different formulas but recorded about 54,000 hits each time.
It would help to narrow the search if you could provide further details such as where each person was born, when approximately were they born, roughly when they died and where were they living when they died (town or county)