Unfortunately I know very little here as William John is a very common name. All I have confirmed so far is that William John, born 1824 in Bettws, marries a Mary (born ~1835) from Ambleston, and that they have a son, William John, in 1858, also born in Ambleston. This all comes from census records from their time in Maesteg and other parts of Glamorganshire.
Perhaps if I start with the William John born 1858 in Ambleston, and work backwards from there?
Mary Evans was just a guess based on the little information I'd seen from Ambleston, but it sounds like I could be completely wrong.