Hi Bunty
Quite a few issues raised there
Post-1911 research is difficult to talk about on here because of the possibility of living people being mentioned and various sensitivities. A few years ago, a cousin and I followed up the descendants of Caroline Parish's daughter Elizabeth Stokes and her husband Henry Roberts. I would say that those living were fairly representative of the population at large in regard to occupation, education, etc. - with, maybe, more university degrees and higher degrees. They had dispersed fairly widely - Canada, Australia and throughout the UK. This was just one line.
I have mainly concentrated on Caroline and her descendants but have ventured into the Durham Parishes because of their obviously close ties with my Chirk family, even into the early 1900s. I've also gone back to Thomas and his ancestors who I've managed to trace back to Madeley - so they were originally English rather than Welsh! My father told me that they had been pit sinkers in Shropshire/Staffordshire who had moved to Chirk in 18th century.
Re Atheliah's son James Parish/Jones, b. 1850 - very interesting information and puts a different slant on things! A Jones family were living next to them in Black Park on the 1851 - HO107/1993/804/8 I assume the Richard Jones would be the son, aged 19 rather than the father aged 54. James is the one I have quoted from the 1901 in Co. Durham.
Re the other James Parish b.c. 1829. The problem here is that there were two both b.c. 1829 - one the son of John and Elizabeth (a) and one the son of Thomas and Ann (b). (i.e. cousins)
(a ) is still at home in Chirk with his parents in 1851 and with wife Mary in 1861 onwards.
(b) is possibly at The Lodge, Chirk in 1851 - a groom to the Ward family. (Thomas Ward ownd Black Prk colliery at the time) It says b. Llangollen but I wonder about the Llangollen birthplace as I don't see him before or afterwards as this. He is, as you say, with Jacob and Harriet in 1871 in Yorkshire. Jacob was with my 2 xgreat grandparents in Willenhall in 1851 but there is no sign of James so the Lodge one looks a strong poss. Many of the 1861 pieces are missing/destroyed and James could be on one of these.
Regards
Gadget
Added - I assume you're familiar with Neville Hurdsman's A History of the Parish of Chirk and a later one about St Martins - mainly pre 20th century but a fair bit on the coal mines.