if this is the family in 1871
Pontymister Tripp, Risca, Mon RG10/5350 folio 163 pg 44
David Williams head widower 57 tin roller b. Carms, Kidwelly
John son 32 miller b. Kidwelly
David head mar 36 tin roller b. Kidwelly
Margaret wife 37 b. Mon, Machen
this family looks a match
1861 Turnpike Rd, Risca RG9/4025 folio 34 pg 25
David Williams head mar 48 tin roller
Jane wife 51
David son 26 tin dubler
John son 22 tin washman
Owen lodger widower 75
all born Kidwelly
1851 Mill Row, Risca HO107/2453 folio 142 pg 10
David William head mar 38 tin roller b. Kidwelly
Jane wife 40 b. Kidwelly
David son 16 b. Kidwelly
Sarah dau 14 b. Carmarthen
John son 11 b. Carmarthen
1841 Old Priory, Carmarthen St Peter HO107/1387/2 folio 52 pg 25
David Williams 30 rollerman
Jane 30
David 5
Sarah 3
John 2
all born in county
had a look on the IGI for any records in Kidwelly. Didn't find marriage or baptism for John, but did find this baptism in batch C058901
David Williams born Jan 1812, bp 6/7/1834 son of Owen & Sarah.
Lodger in 1861 looks to be his father & daughter called after his mother.
Also looks like he was being baptised prior to banns & marriage
David Williams married Jane Morris in Kidwelly 28/9/1834
The baptism batch only starts in 1813, so no baptism for Jane showing, but there are some baptisms to a John & Mary Morris which may be siblings. You can get a copy of the parish marriage entry from the record office and witness names may give a clue to Jane's family
http://www.ancestor-search.info/CRO-Carmarthenshire.htm