I can see the marriage I think you are referring to but do be careful about trying to go any further back without having proof that you are on the right family.
You can order certificates from the GRO https://www.gro.gov.uk/gro/content/certificates/default.asp
Your grandmother's certificate would give you her mother's full maiden name. 
Mar Qtr 1909, Bridgend, Glam, 11a, 1075
John MORGAN
Harriet Anna JOHN
FreeBMD Birth: Mar Qtr 1884, Haverfordwest, 11a, 942
Harriet Hannah JOHN
1891: St Nicholas, Haverford West, Pembrokeshire
RG12 / Piece: 4541 / Folio 67 / Page 8
Benjamin HARRIES 70, widr, Farmer, b Llanwnda, Pemb.
Son; William HARRIES 22, single, Farmers Son, b Mathry, Pemb.
Dau: Phoebe JOHN 37, wid, b Mathry, Pemb.
Gr-Son: Richard JOHN 11, b Mathry, Pemb.
Gr-Dau: Ruth JOHN 9, b Jordanston, Pemb
Gr-Dau: Harriet 7, b Mathry, Pemb. (abt 1884)
1901: The Village, St Nicholas, Haverfordwest, Pembrokeshire
RG13/ Piece: 5133/ Folio: 75/ Page: 2
Benjamin HARRIES 80, widr, Farmer, b Llanwnda, Pemb.
Son; William HARRIES 22, single, Farmers Son, b Mathry, Pemb.
Dau: Phebe JOHN 48, wid, b Mathry, Pemb.
Gr-Son: Richard B JOHN 21 , farmer's Grandson, b Mathry, Pemb.
Gr-Dau: Harriet A JOHN 17, General Domestic Servant, b Mathry, Pemb. (abt 1884)
I know i'm a pain but i'm now trying to find who Phoebe /Phebe married, I'm torn between a William Harries and a Griffith john *aaarghh* any help please?? x