Hi
I have managed to find the obituary of Cornelius Rees
https://newspapers.library.wales/view/3201842/3201844/5/Although in Welsh if you cut and paste into Google translate it does a reasonable job of translating it. In this is mentioned another brother the Rev D. Rees of Braintree and Australia! From this we can attribute David Rees 1806 - 1885 (Victoria, Australia) as another brother. He married a Mary Eliza Curtis (1811-1849) on 24 Jun 1811 St George Hanover Square, London, England and after her death he emigrated with his children to Australia.
Another possible attribution as a brother of Cornelius is William. From Ancestry trees there seem to be 2 candidates; a William Rees (1798) a Farmer/Butcher of Soho, Hengoed who married an Elizabeth Morgan and a William Rees (1791) Farmer of Tynyrheol, Hengoed who married a Catherine James. Of these 2, I currently favour the later as there are some tenuous links with other family members. William of Tynyrheol had a son Hector Rees born around 1825-1828. From other trees Hector married an Anne Robert in 1849 and was a Farmer of Grogwynion(?) Llanddarog and is with his family in the 1851 and 1861 census. In 1871 he is not with them though Ann is listed as married and not a Widow. I think this is because Hector Rees (married) is the lodger, labourer of Llanelly living in Glamorgan with Henry Bowen and his wife Margaret Bowen (nee Rees). Margaret Rees being the daughter of John Rees Blaenhiraeth-Tynyrheol. That John Rees was Farming at Tynyrheol in 1871 and his potential brother William was farming it in 1841 and 1851 provides another tenous link. Arguing against this is that Tynyrheiol in 1861 was not occupied by Rees' and a Daniel Harris, a Carter and William Isaac, a Shepherd’s boy were living there, so there is no continual link in the Rees line. Also Hector was listed as a labourer in 1871 and Farmer in 1851 and 1861, though there is a note in a family tree to say that in August 1868 there was a sale of stock and crop at Grogwynion due to Hector selling up and moving to Llanelly.
This leaves Elizabeth, Hannah and Mary not definitely assigned in the census as children of John of Wayngrychydd, though others have made attributions, but I have no idea what these are based on. If anyone could shed any light on these I would be delighted to hear.