Apparently, some here think it is them. Totally pious and without sin they are; the rest of us deserve to rot in hell.
One thing that I found strange in the movie is that there was supposedly only ONE living descendant of Christ. Supposing (within the logic of the fiction) that Mary Magdalene did give birth to a child. If that child's lineage was fertile enough to have a descendant after 2000 years, isn't it more likely than not that there would be more lines than just the one?
The only smidgen of logic I saw is that perhaps Brown is saying that the secret order had been killing off all these descendants for 2000 years--in which case you still have the illogic that they didn't get that one line.