« Reply #4 on: Thursday 05 March 26 20:11 GMT (UK) »
One of the other posts mentions the baptism for Griffith, the brother of George. It was a non-conformist baptism - Capel y Cwm Calvinistic Methodist Chapel at Cadoxton juxta Neath. Not all non-conformist registers survive, and even less are online. You are lucky that Griffith's baptism was on the first page of a register that was surrendered to the GRO in the 1830s. Luckier still that Ann's maiden name is mentioned. The first page of the register states that it had been in the custody of two of the elders of the chapel and some non-conformist registers moved with the minister so you can understand how they could go astray.
Is this the last census you have for William? Tin Works Row, Llanharan
https://www.familysearch.org/ark:/61903/1:1:Q2W9-678G?lang=enFather George died 24 Nov 1882. Adminstration of his estate was granted to Griffith Morgan & Mary Hughes, wife of William Hughes, two of the next of kin.
I wonder about this William in 1891. Also in Tin Works Row, right sort of occupation, place of birth given the same as that of his new wife.
https://www.familysearch.org/ark:/61903/1:1:HMGL-5T2?lang=en 
Cornwall: Allen, Bevan, Bosisto, Carnpezzack, Donithorn, Huddy, James, Retallack, Russell, Vincent, Yeoman
Cards: Thomas (Llanbadarn Fawr)
Glam: Bowler, Cram, Galloway, James, Thomas, Watkins
Lincs: Coupland, Cram
Mon: Cram, Gwyn, John, Philpot, Smart, Watkins
Pembs: Edwards (St. Dogmael's)
Yorks: Airey, Bowler, Elliott, Hare, Hewitt, Kellett, Kemp, Stephenson, Tebb