I've asked my friend to review the various baptism and burial entries for the offspring of Robert Jones with an eye towards understanding the correct spelling and definition of the name of the two abodes the family lived in from about 1750-1770. As I'd hoped, he has reviewed these spellings and has offered the following:
I read the register entries as Tyddyn Ruffudd and Tyddyn y Dola gwnion
I don't think there is any doubt about the Tyddyn Ruffudd references despite the somewhat idiosyncratic handwriting. Tyddyn Ruffudd translates as "Griffith's smallholding", the Welsh form of Griffith being correctly Gruffudd (u pronounced like English i) and the initial G being lost because of rules of mutation which apply in the language to amend or omit certain letters at the beginning of words in certain circumstances.
Tyddyn y Dola gwnion is, I believe, a name which would now be written Tyddyn y Dolau Gwynion and it translates as "The smallholding of the White Meadows". Very poetic. It seems to be a different place from Tyddyn Ruffudd, unless (not impossibly) it was known by both names.
I feel confident in these interpretations. Now to try and find out if they still existed in Llanfaglan at the time of the 1841 census? The only way to do that is find all the entries for the 1841 Llanfaglan census and check every single page for abodes by these names.
I will be leaving on a two-week holiday at the beginning of this week, so I'm not sure how much I will be able to post, however, if I can monitor responses to this website I certainly will try to keep up.