Hi Roy, I knew from Margaret Treharne's marriage to John Thomas, that her father was William Treharne, a mason from Llanstephan. I am fairly certain that I have the right parentage for her now - William Treharne (1777-1865) and Mary Davies (1777-1855). They were married in 1803 and had a daughter Margaret in 1805. He was a mason, living at Morfa Fach in Llanstephan. Of Margaret's siblings, her brother William followed on in his father's footsteps as a mason in Llanstephan and her brother David died in 1893 while at the Masons Arms.
Something else of interest that I turned up was that Thomas Vaughan's first wife, Jane Davies, died at Pontantwyn Farm in Llangendeirne in 1817 and his first daughter, Mary Vaughan, by his second wife, Margaret Treharne, was born at Pontantwyn Farm in 1825. So Thomas Vaughan was a farmer prior to becoming an innkeeper in 1835.