Huwcyn:
Based on what you shared from "The Early History of the Welsh in the Proscairon District of Wisconsin," it would suggest the following:
Rev. John Robert Daniel (born 1826) was related to the following people in the following ways:
Jane Daniel - his Mom
John Daniel - his Dad
Thomas Roberts - his Uncle
Thomas Roberts' brother, Foulk Roberts - his Uncle
That relationship, as laid out, would indicate that Jane and Thomas and Foulk were first cousins, all of the same generation, and all Roberts. Presumably, all three would've been the grandchildren of Robert John Evan Roberts. At least that's the way I would read it.
If that were the case then that would mean while Thomas and Foulk were the children of Robert Roberts, Jane would've been the child of one of his brothers, which brings us back to the sons of Robert John Evan Roberts and Jane Jones, who were reported in the Hankwitz tree as follows:
John Roberts, reportedly born in 1765
William Roberts, reportedly born in 1767
Funny, when I look at the ages of those involved here, you have two men (Thomas and Foulk), one born in 1820 and the other born in 1826, and both are said to be uncles of a third man (John Robert Daniel) born in 1826. I think we commonly think of uncles as quite a bit older than we, yet in the dynamics of a family tree, you never know. For instance, my wife is an aunt to several nieces and nephews who are older than she.
In many respects, this brings us back to where I started all of this: John Roberts (according to the Hankwitz tree, born in 1765)...or...(according to the combined findings of my friends on Rootschat), a John Roberts born much earlier, approximately 1746, a year that would make him one of the first children of Robert John Evan Roberts and Jane Jones, who were married in 1741.
Footnote:
Huwcyn. I hope it's alright with you, I added a photo of Llanfaglan Church credited to you, posted on the Hankwitz tree website, to my tree and placed a copy in the file for both John and Jane Daniel, as they were married in Llanfaglan. You have the credit attached for the photo.