I have the following on Rev. D.H.T. Griffies Williams' son :
https://newspapers.library.wales/view/3328875/3328878/14/%22D.%20H.%20T.%20G.%22The Cambrian
15th October 1836
Family Notices
BIRTHS
On the 28th ult., at Llwynhelig, Carmarthenshire, the lady of the Rev. D. H. T. G. Williams, of a son and heir.
BURIAL RECORDS
6th January 1838, Aged 15 months
H.H.G. Williams, Llwynhelig
Clergy : Rev. Thomas Morgan, Llanfynydd
Interesting that you found he was first buried elsewhere and then reburied in Llandyfeisant. As far as I know he is not mentioned on the gravestone.
https://newspapers.library.wales/view/3419813/3419815/27/LlwynheligSaturday, 11th January 1879
THE LATE MRS.WILLIAMS, of LLWYNHELIG
On Tuesday the remains of Mrs. Williams, of LIwynhelig were interred at Llandyfeisant churchyard. The deceased lady was advanced in years, and had been bed-ridden for many years. She was very highly connected, being a sister to Lady Charles Russell and to Mr. Evans, of High Mead, Cardiganshire, and was grand-daughter of the late Lord Robert Seymour. Her husband, the Rev. D. H.T. G. Williams, late vicar of Llandyfeisant, died in April, 1877. The funeral was strictly private, and the respect in which the deceased lady and her family were held might be inferred from the fact that there were present at the funeral the members for the county. Viscount Emlyn and Mr. John Jones, also Mr D. Pugh, Capt. Lewis, Capel Issac, Mr Ellis, Llangadock, Capt. Phillips, Head-Constable of Carmarthenshire, Dr Davies, Llandilo, &c. The undertaker was Mr. O. James, draper, Llandilo.
https://newspapers.library.wales/view/3433543/3433550/193/Llwynhelig Saturday, 13th July 1907
Miss Caroline Williams, Llwynhelig
At Llwynhelig, Llandilo, on Sunday, the death occurred of Miss Caroline Williams, youngest and only surviving daughter of the late Rev. T. H. J. G. Williams, vicar of Llandyfeisant and Llanfihangel-Aberbythych, and rector of Penboyr. On her mother's side she was a niece of the late Lady Charles Russell, and on her father's side of the late Sir Erasmus Williams, a cousin to Colonel Davies Evans, Highmead. During the South African wars she was probable alone amongst members of county families who was a pro-Boer. Of recent years she had lived a very secluded life.
https://newspapers.library.wales/view/4470749/4470752/25/Penboyr23rd April 1877
DISTRICT INTELLIGENCE
THE LATE REV. HERBERT GRIFFIES WILLIAMS who died at his residence of Llwynhelig on the 8th inst., aged 69, was the son of the late Sir. George Griffies William, Bart., Llwyngwonna Park, Carmarthenshire. He married Anne Gertrude Frances, daughter of William Davys of Penylan, by Elizabeth, eldest daughter of the Lord Robert Seymour, of Taliaris Park, and leaves a family by whom he is deeply lamented. The deceased was rector of Penboyr, Vicar of Llanfihangel Aberbythich, also of Llandefeisant He was interred on Tuesday, the 15th inst., in the presence of a numerous assembly of relatives and friends, the service being conducted by the Rev. John Griffiths, D. D vicar of Llandilo, at the church of Llandefeisant.
https://newspapers.library.wales/view/3371272/3371278/109/27th November 1897
GRIFFIES-WILLIAMS
DEATHS
On Sunday, November 14th, at Llwynhelig, Carmarthenshire, Clarissa Delme, second daughter of the late Herbert Thackeray Griffies-Williams, and grand-daughter of the late Sir George Griffies-Williams, Bart., of Llwynywormwood Park, in the same county.
https://newspapers.library.wales/view/4358971/4358979/42/11th December 1908
DEATHS.
THOMAS
At 20, Boulevard de Chateau, Neuilly, Paris, Elizabeth, widow of Bowen Thomas, Esq., and eldest and only surviving daughter of the late Rev. D. H. T. Griffies-Williams, of Llwynhelig, Carmarthenshire, aged 78.
I have copy of the Baptismal & Burial Records 1784-1812 and Baptisms 1813-1916 and Burials 1813-1970 for Llandyfeisant Church. What would be the best way for me to send them to you? Have a look at the website friendsofllandyfeisantchurch.org