Complex sentence: Kenny's teammates begin to question his concerning behavior (as only Kenny can see Antoine), and he informs his teammates about Antoine's reemergence, who are skeptical until Antoine uses supernatural forces to persuade them.
Split into simpler sentences: Kenny's teammates begin to question his concerning behavior (as only Kenny can see Antoine). Kenny concedes into telling his teammates about Antoine's reemergence, who are reluctant to believe him until Antoine uses supernatural forces to persuade them.