Nearest I can see to the "Barry & Penarth railway" is the Cardiff, Penarth and Barry Junction Railway - see
https://www.railscot.co.uk/Cardiff_Penarth_and_Barry_Junction_Railway/. This was opened in 1887 - presumably by its own company - then taken over in 1889 by the Taff Vale Railway. In 1923, the Taff Vale was absorbed into the Great Western Railway. Part of the line is still open to Penarth.
https://en.wikipedia.org/wiki/Penarth_railway_stationAccording to David Hawkings'
Railway Ancestors, there are no known staff records from the CP&BR.
There are some staff records from the Taff Vale at the National Archives at Kew in class RAIL 684, and plenty from the GWR in various classes. Two
GWR pieces catch my eye - RAIL 264/305 & /306
Reference: RAIL 264/305
Description: Register of men (late Taff Vale rly.)
Date: 1895-1923
Held by: The National Archives, Kew
Reference: RAIL 264/306
Description: Register of men (late Taff Vale rly.)
Date: 1886-1923
Held by: The National Archives, Kew
Both are noted as "available to download from Ancestry". Your best bet is simply to search Ancestry using the index. Depending on when GGF joined, he might have started working with the GWR, in which case he won't be in the RAIL 264/305 & /306 pieces anyway.
I have
no idea how comprehensive the RAIL 264/305 & /306 pieces are for ex-TVR staff still around in 1923. And I have
no idea how comprehensive the GWR records are for staff who started their careers with the GWR.
Best of luck.
PS - I also have my doubt that Ancestry have imaged and indexed as much as they claim of the railway staff records at Kew.