edit to add: can you make out the place of birth for Edward in the 1851 census?
It looks like Llaneilian to me - with Llandyfrydog crossed out.
Thanks. It's proving impossible to prove for sure that this Edward is Henry's father. I believe I have found one of the witnesses to Henry's wedding, a Griffith Roberts.
This Griffith Roberts, born Tynymynys, Amlwch, Anglesey, 1823 to Thomas Roberts and Gwen Thomas lives at Tynymynys with his father Thomas in 1841, very close to Edward and Grace Parry (two pages ahead).
Griffith marries Elizabeth Owen (who's father is transcribed as John Owen) in 1847. Sadly the document is heavily blotted, it's very difficult to read.
From 1851 to 1881 he is recorded as living at Corwas, Llaneilian. Initially Griffith works on the mines as an Engine Driver, just like Henry. He's a farmer in 1881 and dies before the 1891 census. His wife continues to live at Corwas and dies sometime between the 1901 and 1911 census presumably.
Note that in the 1871 and 1891 censuses, Corwas is listed beside Glanyrafon.
Griffith's father Thomas marries Gwen Thomas at Llandyfrydog, Anglesey, Wales in 1808. Witnesses are William Thomas and Samuel Roose.
I'm yet to check the baptism records of all the children but on the balance of probabilities I think Griffith is Henry's cousin on the side of their mothers, Gwen and Grace Thomas.
The smoking gun would be to match the baptism records of Gwen and Grace above. However I can only find Grace's baptism record which is think is 1791, daughter of Wm Thomas and Ellin.
Interestingly, Griffith's father in law John Owen (who lives at Corwas in 1841,51) ends up at pengraigwen, Llandyfrydog in 1861.
I think this is suggestive that Henry is Griffith's cousin. My mother recorded Henry's grandson Henry Parry as born at pengraigwen, 1883. I think she may have the birth certificate. Will get onto her. This pengraigwen is next door to Tyn y Lon which I think is the Tyn Lon where Henry lived.
Thought the following may help to illustrate this. This is Henry's (the one born 1883) son Hugh with Ellen Parry his grandmother and Lily Elizabeth Parry (nee George) his mother in 1926.