Hi Badgirl,
just to throw a spanner in the works!!
Are there 2 Rees Griffiths in your search as I found one living with his mother Tydfil Griffiths at Pen-y-gaun, Llantwit juxta Neath.
Household;
Tydfil Griffiths age 62 formerly woocutters wife
Rees age 32 coal miner
Lewis age 15 Blacksmith
Hannah age 22 Dressmaker
David age 18 coal miner
Charles age 24 Blacksmith.
This is from 1861.
This Tydfil Griffiths died 2nd qtr 1881 age 84 Neath vol 11a page 324.
Could your cousin be mixing up families and you had the right ones?