The Holy Bloodline myth derives from the semi-fictional pseudo-history book Holy Blood and the Holy Grail, which used poor scholarship and unreliable sources to develop the idea that Mary Magdalene married Jesus and had children by him who eventually gave rise to the Merovingian royal house. The claim has little textual support beyond some ambiguous Gnostic references to the pair kissing. Peter of les Vaux-de-Cernay, writing in the Historia Albigensis 10-11 before 1218 said that the Cathars considered Mary Magdalene to be the “concubine” (but not wife) of Jesus, not because they had special knowledge but because they identified the pair with the incident of adultery in John 8:3. The other support for the claim comes from the special veneration given to Mary Magdalene in southern France, where a medieval tradition, first recorded by Sigebert of Gembloux in the Chronicon sive Chronographia (entry for 745) around 1112, says that Mary Magdalene traveled to Gaul and was buried at Aix, and later Vézelay. While this legend grew like kudzu in France (becoming a key chaper in the famous Golden Legend), it was clearly not the original tradition, nor does it have anything to do with holy children. The Eastern churches held that the Magdalene was buried in Ephesus (Modestus in Photius, Biblioteca 275), which even Western writers—in France no less!—agreed with until the High Middle Ages. Gregory of Tours, for example, writing in his In gloria martyrum 1.30 in the sixth century CE reported on the Magdalene’s grave at Ephesus.
So what does Wolter have to say about McGowan Coppens?
I have never met Kathleen so I have no opinion about her. She's seems like a nice enough person during her appearances on the two Oak Island episodes that I watched, but I know nothing else about her.
I don't think it's fair to say she's not a legitimate researcher simply because she believes she is descended from J & M; she might very well be. Just as it's also possible there could be thousands of other people who are. Neither you or I know the answer to that.
While a match would not prove either claim, failure to find a match would do much to logically disprove one or both claims, so perhaps that’s why we aren’t likely to see anyone agitating for this very obvious step toward confirming or disproving the largely baseless Holy Bloodline claim.