Could you be related to Dylan? It’s certainly possible! He came from a very large family – his grandparents and great-grandparents, for example, had more than thirty siblings between them.
Both Dylan’s maternal and paternal ancestors came from Carmarthenshire in west Wales. His mother’s family were from the Llansteffan peninsula, farming in the countryside around Llangain and Llanybri. His father’s family came mostly from Brechfa and its hinterland and they, too, were farmers.
The most useful starting point in understanding Dylan’s family tree is chapter one in the book Dylan Remembered 1914-1934. It provides basic genealogical information on family members from Dylan’s great-grandparents onwards, for both sides of his family eg dates of births, marriages and deaths, names of children and occupations.
Dylan Remembered 1914-1934 was published in 2003, and since then a good deal more work has been done on his mother’s side of the family. Two sets of Dylan’s maternal great-great grandparents have now been identified, as well as three sets of his great-great-great grandparents, and this has produced a large volume of new genealogical data. You can find this material, together with family trees, at https://sites.google.com/site/dylanthomaspeninsularity/home
You should also go to this link if you think you might be related to Dylan’s family through marriage. For example, it has a number of pages on the family tree of Jim Jones Fernhill, who married Dylan’s aunt Annie.
The pages on this link will also help if one of the clues to your family’s history is the name of a farm. There’s a map at the link that shows the main farms in which Dylan’s maternal relatives lived. You can also use the search function to search for the names of these farms in the various papers at the link.
The census returns for most of the family farms are given at the following two links: https://sites.google.com/site/dylanthomasandhisaunties/returns-of-the-census-for-the-family-farms
Information on Dylan’s Ferryside, Llandyfaelog, Pontardulais and Port Talbot relatives can be found at https://sites.google.com/site/dylanthomasandhisaunties/home
Dylan also had relatives in New Quay, who had moved there from St Thomas in Swansea; information on these is available in The Dylan Thomas Trail (Y Lolfa, 2002), pp105-109 with photos on pp112-115.