Here's what I believe to be the marriage of John and Sarah:
8 Feb 1817 at Ruabon, John, of the parish of Llangollen, and Sarah of the parish of Ruabon, by licence. Witnesses: Richard Edwards and Elizabeth Roberts (all signed)
I've found some info on Joseph and his 4 siblings:
Frances, born 18 May 1817, baptised 12 Oct 1817 in Overton
Joseph, born 23 April 1820, baptised 30 Dec 1821, married Sarah Davies nee Roberts at Ruabon on 21 Oct 1839, died May 1879
Richard and Thomas, twins, born 23 April and baptised 2 June 1822 - Richard married Sarah Allen in Overton, had 9 or more children and died in Overton in 1894. Thomas, possibly in the workhouse in Wrexham in 1891, but nothing else found so far.
George, baptised on 8 Jan 1826, married Eliza Henshall in Shropshire in 1850, had 6 or more children, last seen as a widower in 1901 aged 74 in Whitchurch, Shropshire (recorded as deaf from birth).
No obvious burials in Overton for John or Sarah (or daughter Frances), but maybe they moved away and had more children. Neither appears to be with any of their children. No luck looking for John and Sarah in 1841 or 1851 but difficult without knowing their age or place of birth. I've also looked for John born Llangollen but nothing there either.