Seneschal of Dol's sons were Alan and Flaad ( hereditary Stewards of Dol). This was the Vine of Judah for the first 1000 years after Joseph of Arimathea and James the Justus. The original founders of the Grail Keepers/Knights Templar.
The vine spreads even farther to Alan Fitz Flaad de Hesdin, Baron of Oswestry. Alan's sons were William and Jordan Fitz Allen. The Baron had a daughter Emma who married Walter, Thane of Lochaber, the son of Banquo. Emma and Walter's son, Alan of Lochaber married Adelina the daughter of Alan Fitz Flaad. Alan and Adelina were the parents of Walter Fitz Allen, the First High Steward of Scotland.
This brings the connection of Banquo and the Fitz Allen's together. Both families were hereditary Knights Templar and Order of Sion (Jerusalem). The vine branched out to become what modern day history calls Jacobites.