Hello Pamela.
Im Not sure where the notes would be now, Maybe you could try the local archives in Ebbw Vale. Pontypool is an English speaking area now, but at the time it was very mixed, so it could be either. Do you have an address of where they lived? If they lived in the Trevethin Parish, they wouldnt have had to travel to Blaenavon for work in the mines, there was plenty on theyre doorstep in Pontypool.
The old Quaker building in Trosnant Pontypool is still there ( Albeit not the original) But it has for the last 60 years at least been a masonic hall. Just behind this building overlooking an old Dram Road in Pontypool Park is a Quaker Burial ground. The grave stones were still in place up untill last year, and are now resting against the building. Last year their were about 20 of them, and they are quite hard to read but date from the late 1700s to 1800s. Il try to find out what quaker buildings were in the Garndiffaith area as you mentioned High St up the Garn.