I looked for David Harries in 1841, but no luck. I found his 1851 Llanelly Queen Square neighbours, but there weren't any glovers/skinners, let alone any called Harries/Harris. (NB. Queen Square is called King Square in 1841.) I thought he might be in Abergwili and there is a David Harries there, aged 25, an Ag Lab, living in an outhouse which didn't seem right, somehow!
However, this could be David's parents and siblings:
1841 HO107/1387/1/6/4
New House (Goityeadno?? Pound?), Logincoch, St Peters, Carmarthen, CarmarthenshireJohn Harris, 50, glover, yes born in county
Anne Harris, 50, yes
Jane Harris, 20, yes
John Harris, 20, skinner, yes
Anne Harris, 20, yes
Thomas Harris, 15, skinner, yes
Henry Harris, 14, skinner, yes
Sarah Harris, 11, yes
Benjamin Harris, 6, yes
1861 RG9/4113/16/26
King Street, Llanelly, CarmarthenshireDavid Harris, head, 50, glover & leather draper, b. St Peters, Carmarthen
Margaret Harris, wife, 35, b. Abergwilly, Carmarthen
Jane Harris, dau, 13, b. Llanelly, Carmarthen
John Harris, son, 9, b. Llanelly
Thomas Harris, son, 7, b. Llanelly
Sarah Harris, dau, 4, b. Llanelly
William Harris, son, 2, b. Llanelly
1861 RG9/4141/64/15
Tanerdy? Road, St Peter, Carmarthen, CarmarthenshireBenjamin Harris, head, 26, glover & skinner, b. St Peters, Carmarthen
Rachel Harris, wife, 28, b. Abergwili, Carmarthen
And this is interesting, and a bit confusing!!
1871 RG10/5467/31/7
7 Union Building, Llanelly, CarmarthenshireDavid Reynolds, head, 29, carpenter, b. Llanelly, Carmarthen
Jane Reynolds, wife, 23, b. Llanelly
Mary S Harries, step-dau, 3, b. Llanelly
David J Reynolds, son, 9 mths, b. Pentre y strad, Glamorgan
I can't find the rest of the Harries family with any certainty. There are individual Harries children dotted around but there's nothing to tie them into David and Margaret's family.