I have the exact date of death from the parish records but again it states the abode as just either Lydney or Purliers. It does not state the cemetery where they are buried.
As to the marriage parish record there are two witnesses to each of the marriages but in all cases, one witness was the church clerk and the other witness's name doesn't show up anywhere within the family nor near the couple in the 1841 census. I am in the process of tracking down the banns register for all 3 marriages to see if anything shows up. Other than this, I am not sure which direction to take.
It's more usual for a parish burial register to record the date of burial rather than the date of death. The entry in that register would have been made by the priest or sexton or parish clerk on the day of (or very soon after) the burial and the entries often give some family information (eg son of X) which, if the registers are in reasonably good condition, are available to read today.
Conversely, it's more usual for a tombstone to record the date of death rather than the date of burial. Tombstones are usually made and set up quite some time (months or even years)after burial to allow the ground to settle. Some graves never have tombstones because families could not afford them and they deteriorate or are removed to make room for others. So whatever information was recorded on any tombstone is very likely to be eroded or destroyed.
I have just googled 'Lydney cemetery' and the third hit in the list was for Saint Mary's Lydney churchyard and cemetery. The website link includes some inscriptions from some graves in that place. Perhaps that is where you got your details from. If that is so then it follows that those graves are in Lydney Saint Mary's churchyard and cemetery. If you got your information from the parish burial register then it is almost as certain that the grave is in the churchyard/cemetery of that parish unless it says to the contrary. This church is the only C of E church in Lydney that I can find.
I don't know a place called Purliers and I can't find it on Google.
It sounds as if you are having a very tough time with your searches which I guess is inevitable if you are so distant from the records. I'm afraid that in my experience banns registers only show the names of the couple intending to marry and their parish and the dates on which the banns were called so I don't think they are likely to help you. I hope I am wrong.
Perhaps if you quote the names of the people you are trying to trace someone will help
