Hi David,
My G/Grandfather Evan Rees was born in Llangyfelach in (approx) 1838. He married Margaret Davies in Llangyfelach in 1859, and on the 1881 Census for Wales they are living at 18 Welcome Street, Swansea with their 7 children:
Evan Rees 42yrs Occupation: Copperman.
Margaret Rees 43yrs
John Rees 22yrs
Sarah Ann Rees 19yrs
Margaret Rees 14yrs
George Rees 13yrs
Elizabeth Rees 9yrs
Selina Rees 4yrs
William Rees 2yrs.
The Margaret Rees, aged 14yrs on the 1881 Census was my Grandmother. I know that Elizabeth and Sarah Ann emmigrated to the USA, but I don't know what happened to the rest of them.
I've found Evan Rees's parents, (Evan and Anne Rees) on the 1841 Census for Wales, & they both seem to have come from Llangyfelach too. I can't see any links to Llangynwyd, but who knows?
Best Wishes,
Romilly.