I thought it was only 1 on the VoR as one was in black and the other in green.
I agree-
My photographs show no.7 in blue, no. 8 in black, no. 9 in green livery.
I think it was 3 and all on the Vale of Rheidol.
I concur with your view and I would add that after steam traction was officially withdrawn by British Rail, all three of the locomotives were then repainted in the corporate British Rail "Rail Blue" livery that incorporated the double-arrow symbol. This livery was retained by all three locomotives until 1981 when locomotive number 8 was repainted in a "heritage livery".
They carried high quality Welsh coal to supply the RN fleet at Scapa Flow. This would have been over many pre grouping lines which where run by the government during WW1 so not sure what answer you need for the name of the railway.
Didn't some also run from the South Wales Coalfield via the GWR to Banbury, and then transferring to the GC for the journey to Immingham and other East Coast ports?
It was the highland railway. Troop trains at a guess.