I now have Hughes/Williams marriage certificate Dolgelly AMJ 1896 11b 673. Date 25/4/1896
Mary Elizabeth Williams Widow age 21 of Brynllwyd, Corris, Talyllin. Father William Lloyd (Dec'd), farmer.
Thomas Hughes Widower, age 27 of Greenfield Terrace Corris, slate quarrier. father Griffith Hughes (dec'd) farmer.
Witnesses Henry R Jones and John Rogers.
So this confirms previous input from Gadget and Roger - Mary E's father was William Lloyd which fits with William and Grace Lloyd as her parents.
What is a surprise is that Thomas Hughes was a widower on marriage. I wonder if that explains the other 2 children who died (of the 5 born by 1911) - perhaps they were his from a previous marriage. I know the census asks for "children of this marriage" but it already looks as if Mary included William Lloyd Williams to make 3 living.
The 1911 census raises more questions than it answers because Mary E states she is Married not Widowed but there is no Thomas present and I can't find a record for him. She has also moved away from Corris to Abergarfon Isof, Pantperthog which is in Machynlleth district. However, her ages through the census returns and the 21 on marriage are consistent with a birth in Dologelly OND 1874 11b 391
William Lloyd farmed a large farm at one time. In 1871 the Brynwllyd farm was recorded as 337 acres and he was employing a farm labourer
Grace was a Davies from Llanwin, Montgomeryshire- in 1901 she was by then a widow with her brother Joseph and sister Margaret living with her in Glanynant Corris. There were 3 families in Glanynant including Thomas and Mary E Hughes.