"If the assumption that Mr. Reyes did a deal with Fung and Tenor is true, do you think shareholders could sue him if his deal got him more than other shareholders?"

We would sue the company for fair value. Reyes / Fung / Tenor could possibly have a criminal complaint against them. However, this is an outrageous claim and if your defamation is based purely on conjecture you may want to retract it. Don't think that by using "assumption" you are immune from defamation.