Well, I have a suggestion for John but I'm not really sure, think you might need his marriage cert to confirm. Hengoed is next to Pembrey.
1881 Casthouse, Hengoed RG11/5375 folio 143 pg 39
John Griffiths head mar 33 tinplate worker b. Carms
Jane wife 24
Mary Anna dau 2
Martha dau 3 weeks b. Llanelly
There is a bit torn from the corner of the census page and only Martha has a place of birth. Ancestry has Martha as 3 years old, but it's definitely weeks.
Only one Martha Griffiths registered in Llanelli around that time
Martha Ann Griffiths june qtr 1881 Llanelly vol 11a pg 799
Only one likely marriage as well
John Griffiths june qtr 1878 Llanelly vol 11a pg 787 with Jane Emmanuel on the same page.
1891 3 Stradey Rd, Hengoed RG12/4496 folio 135 pg 12
John Griffiths head mar 43 tin worker
Jane wife 37
William son 12 scholar
Martha dau 11 scholar
Esther dau 6 scholar
Beatrice dau 4 scholar
Rees Emmanuel boarder 60 coal miner
Esther boarder's wife 67 b. Llangennech
Lizzie boarder's dau 17 rubber at tin works
William boarder's grandson 5 scholar
all born Llanelly except where stated and all Welsh speaking
Now, where is Mary Anna and where did William come from? I think one of them may be a mistake, or they could have been staying with relatives on alternate census nights in order to confuse us.
1901 3 Stradey Rd, RG13/5090 folio 88 pg 3
John Griffiths head mar 53 tin plate worker in tin works b. Pontyberem
Jane wife 46
M Ann dau 20
Esther dau 16
Beatrice dau 13
William Rees son 12
David John son 10
Henry son 6
Rees Emmanuel boarder single 71 collier cutter retired(?)
William Emmanuel boarder 15 tin worker in tin works
all born Llanelly except where stated. John giving Pontyberem as his place of birth is a bit of a spanner in the works. It's yet another area of Llanelli. I've had a look on earlier census entries and I can't find a John b. 1846ish living in Pontyberem or giving it as his place of birth.
As I said before, the marriage cert would confirm John's father.
I do like families who have the in-laws living with them even if they do call them boarders. Makes identifying the marriages so much easier.