There were actually two versions of "Holy Blood Holy Grail" the book. The first one had a detailed genealogy, but my copy was destroyed in the Los Alamos fire of 2000. I wanted to reread it while I was studying Stuart genealogy, and so I bought another copy, which was a total rewrite and had no complete genealogy in it. I lost the second copy in a move, and was not sorry to lose it, as it was an inferior rewrite, and I thought at the time it was written to accommodate two theories, one the new Da Vinci Code theory, and the other theory that a certain man from the continent was the actual pretender to the Stuart throne (the latter having later been shown to be a complete fraud).
I feel there probably are people living (many) who are descendants of Jesus' family. Roman Catholics believe Mary had no more children after Jesus, but Protestants believe there were several brothers and at least two sisters, since the gospels refer to his "sisters" plural. Catholics think these are cousins rather than sisters. The most prominent brother was James, who became head of the church at Jerusalem, and who apparently was not a follower of Jesus before His resurrection. If these were brothers and sisters rather than cousins, it seems very likely there were descendants, at least a few, although the church was persecuted in the time of James, and James himself was killed.
So I think that even if Jesus had no children, He probably had nephews and nieces. So there you have a "bloodline" of sorts.
I do not think it negates Jesus' divinity if He married and had children. The big problem would be, in my thinking, that there would be children
who were not holy at all, and who would use their descendancy to lord it over everyone, which God could not have allowed. So if He had children, this would have been top secret. And never have leaked out in such second-rate versions as the Da Vinci Code. His children would not be holy in the sense that He was, not being divine, but just human. Jesus had both a divine and a human nature, but these children would have only human natures, even if they had noble natures.
Concerning the descent of the British royals from ancient Israel, it is traced through an Irish queen who was one of two daughters of Zedekiah who escaped slaughter when the sons of Zedekiah were murdered by the invader. The legend is that the Prophet Jeremiah and his scribe Baruch
took the girls away. They went to Egypt first, where one of them married another Jewish royal person--they being both descended from Judah,
and the princess being descended from King David. This prince whom she married took her back to Ireland, where there was already a Jewish
community of long standing, and there they ruled from "Tara". This legend states that Jeremiah is buried there in northern Ireland, and I have an
on-line Christian acquaintance who states that he has visited the grave of Jeremiah, which is available for all to see.
The second daughter of Zedekiah to escape from Israel is said to have settled in Spain and married there. The names of these girls have been given variously, so I am not sure which is the correct form. "Tia Tephi" is mentioned, but also "Zara", which is the name of Princess Ann's daughter---did Ann choose this name remembering a legend?
Eleven per cent of Irish people in Ireland are said to have Haplogroup J1c on their mitochondrial descent, linking them to both Jews and Arabs of ancient times, underlying the overarching non-royal story that there was a group of Jews who migrated early to Ireland. My maternal haplotype is J1C2b, which I found out through a genetic study done by a Stanford-related group. My mother was Irish, and was a part of this particular
group. This is not a royal descent, no claim there.
The Stuart family came to Scotland through England (Shropshire) where they lived for a couple of generations after crossing the channel--they had been "prime ministers" of Dol in France. Then they moved on to Scotland, being forced out of England by politics and warfare in the fight
over the succession of William the Conqueror. Were they originally of that group which came through Ireland? I think it is possible. But there were other families in Scotland, including the Stuarts, who signed the Treaty of Abroath in the l4th century and claimed they had arrived in Scotland through the migration from Scythia to the Holy Land, to Spain, to Ireland, and on to Scotland. Complex, with many families involved. But that is some of the background of how the Stuarts claim descent from King David of Judah. They many have a slightly different version, but
that is the outline.