None. There is zero chance that any of this is accurate. First, let's do some analysis as to whether this is a good source. It's making some seriously bold academic claims, but neither of the authors is a scholar, and the press publishing this isn't an academic one. That should raise some red flags - would you trust a book that claimed to have proven perpetual motion to be possible if it wasn't written by scientists or published by a scientific press? These kinds of thing should make you skeptical. Claims this bold need to be peer-reviewed and discussed within the academic community. That the authors go directly to the public, rather than engaging in that conversation, generally means that their claims can't stand up to the evaluation of scholars.

Second, to call this a fringe conspiracy theory would be a little generous. This is so out of line with the state of scholarship that it's difficult to know where to start. The FAQ has a number of questions about Jesus and the early Christians which might be useful to you, in particular these two: u/talondearg on the historicty of Jesus, which is widely accepted by scholars, and also u/talondearg on Christianity's development from its roots.