Vaguely possible family on the 1911 census?
https://www.ancestry.co.uk/interacti...nSearchResults
Wynnstay House, Garth Hill, Taffs Well, Pentyrch, Glamorgan
Benjamin Rees Head 52 Wid 5 children born alive, Coal Salesman, Llanboidy Carmarthenshire
Katherine Rebecca Rees Dau 22 Single Cardiff
David Edgar Rees Son 19 Auctioneer's Pupil Llanelly Carmarthenshire
Mary Louise Rees Dau 17 Kilbarchan NB
Benjamin Alan Rees Son 16 Clerk Johnstone NB.
David, Mary, and Benjamin jr could conceivably be Dewi, Mari and Ben. Will have to trace them back to see if there is a Williams connection.