i am trying to refute those like Springmeir, Icke, Baigent Lincoln Leigh etc who claim that they comprise an alleged 13th satanic illuminati bloodline with descendants of Jesus...

Below is a link about descendants of Julius Caesar. May not seem relevant at first, but it does help explain why fiction like Dan Brown's is silly, naturally speaking.

"Statistically speaking, if someone from two thousand years ago has any living descendants, then virtually everyone from the region is probably descended from them."

The reason: until relatively recently, many women and children died in childbirth and just one instance of that could end a line of descendants. If a line of descendants DID survive ~2000 years, it wouldn't be just a small group of people, because a small group would involve inbreeding which would have significant health consequences in 2000 years. Several European royal lines have issues from inbreeding in only a few hundred years.

https://talesoftimesforgotten.com/2019/08/30/are-there-any-living-descendants-of-julius-caesar/