These are very confusing lines and it seems the only real source is:
http://www.ancientwalesstudies.org/id21.html
On that site, it says Ednyfed was the son of Anwn Dynod and shows him in one of the charts as this:
279 Maxen Wledig (not Magnus Maximus)
l
302 Antonius Donatus (Anwn Dynod)
l
330 Ednyfed
Notice it lists his father as Antoonius Donatus (Anwyn Dynod) and not as Antonius Donatus Gregorius. And it's very specific that Maxen Wledig is not Magnus Maximus.
Reading the info on Maxen Wledig at this site, it does say: "Virtually every account of the man whom the Welsh called Maxen Wledig identifies him as Magnus Maximusa", BUT if you read further, he explains that 2-3 different Maxens have been merged into one person and that's why there is conflict with the dates and gives examples and states " It is more likely that he figures in the old stories as yet a third "Maxen"
And at the end of the page, he concludes:
" Virtually all of our reconstruction of events is simply conjecture; history is silent on these matters. But any accounts which fail to take chronology into consideration simply cannot be accurate. If the events reported by Geoffrey occurred at all, they must have encompassed the lives of more than a single Maxen."
So, it seems there is no concrete validation for he connections beyond this Ednyfed's father who was known as Antonius Donatus (Anwn Dynod) and whose father was known as Maxen Wledig (not Magnus Maximus). This would mean that this profile has the incorrect name of Antonius Donatus Gregorius:
and that basically everything beyond Ednyfed ap Anwyn Dynod ap Maxen Wledig is conjecture based on jumbled up history that can't be proven.