1)Report that x, y, and z sources say these books are co-written. I.e. write in a neutral tone not implying any judgement on our part, what other, reliable sources say.
2)speedy delete- A7, does not assert importance or significance. (Or whatever is the allowed quickest deletion process for a library.) Leave a polite message to the author, explaining what he did 'wrong' and encouraging further edits.
3)'You' would be engaging in original research. Report in the article that he calls himself "world's greatest orchid man" and let that give the reader the measure of him. What do reliable sources say about him is what's important. I would report both what his own 'spin' on it is, and what all reliable sources say, in an NPOV manner.
4)Check that it is not true.:) Then, seek to reason with the editor and 'educate' him about what we allow on wiki- users respond surprisingly well if they perceive that you are trying to help them meet the standards that get their content included (even if it never reaches that state.)
5)Has the theory been in many sources? If only a few or the sources are not very reliable, those at AfD would usually respond favourably to an attempt to delete this. There should only be one article on it- more are unnecessary. Allow all the reliable sources that discuss it to be mentioned, and maybe an organization of fans of it (the most prominent org) to be mentioned too. Say that no peer reviewed studies have validated this. Problem solved.:)
6)The belief should have its own article, only.
7)Block him if he keeps reverting. He is not here to create an encyclopedia but to have what's in effect a vanity claim for his family here. Probably this will be the only, or one of few, articles he edits.
8)Suggest that he contributes to the actual articles such as NPOV etc, and discusses his thoughts there. If he continues to, in effect, make a pretence to be jimbo or an admin, and attempt to mislead other users, block him.