Thanks for the info. I think the death record for Gwillym is incorrect. I have contacted both cemeteries and Riverside sent me a list of all Williams and Gwillym nor Rose where listed.
I also contacted St. Mary's and there is a Cuff Plot in the St. Paul Section #63 that has Thomas Cuff and Mrs. Thomas Cuff (Catherine Doyle), Mr. and Mrs Dovey (Michael Dovey and Phoebe Cuff) Mr. and Mrs. Wm Williams (I am going to guess this is Gwillym and Rose) John "Jack" Williams (one of their sons cremated) and unknown Williams (I am guessing either one or both boys that died in infancy)
I have asked the cemetery if there are markers and if they could send me a map. It would be a shame if there was no markers