I read Holy Blood, Holy Grail, and the two sequels. I refrained from making any statements as to the veracity of their conclusions or the solidity of their researched papers.
The first half of The Messianic Legacy deals with what is known about the historical figure of Jesus, twin brother of Thomas (an Aramaic word for "Twin") and eldest brother (heir apparent) in the family.
What I find saddest, though, is the loss of Judas and his role in the great drama that apparently played out two millennia ago. Jesus said to Judas, his youngest brother, that he wanted him to do what he couldn't: be the bad guy. Not in the story. But for all history and for all time. Jesus apparently someone he could trust to deliver him to the authorities. Judas voluntarily took on the role.
(The main crux of the series of books is that Jesus didn't die on the Cross, which was apparently placed on private land (Peter's, who was pretty rich) where the body swap was made: some poor sap who became the anonymous subject of a snuff drama. Not so astonishing to any Muslims, though, as this assertion is confirmed in THEIR book of DIVINE TRUTH, specifically Book 4 (Women), near the end. But I digress.)