Can't see anything on Stephen Matthew's parentage. Perhaps there's only the one Geoffrey, the Welsh one.
The story seems to be that Richard Newberry married Grace daughter of John Matthew and had lots of little Newberries all in Yarcombe, Devon. But Richard came from Dorset, though with no dates or parents.
The Newberries are made to descend from suitably posh Newburghs, but not by the obvious route. Instead, John Matthew's mother is made to be a Newburgh, born in Devon for no apparent reason. Then her father leaves his kids in Devon and is mysteriously drawn to Dorset to die in the same village his great-granddaughter's husband will be mysteriously born in 40 years later.
My theory is reincarnation.
Actually it's a rescue attempt. The original royal descent of Richard Newberry got disproved, so the Matthew detour is Plan B.