A Inquisitor doesn't normally work in conjunction with others, especially with those from different ordos. But on occasion there exists needs for the combined intellect and resources of multiple such individuals, to form a conclave of Inquisitors:
Even within an Ordo, fields of endeavour seldom overlap completely. Each branch, after all, encompasses an almost infinite potential for study and investigation. Even so, Inquisitors sometimes band together into a loose association called a conclave. A conclave is assembled at the request of a respected Inquisitor, who seeks to pool the skills, knowledge and resources of his peers in order to oppose a threat too great for a single Inquisitor to face; an Ork Waaagh!, a daemonic incursion on a massive scale, or a plague of heresy.
-- Codex: Inquisition. "The Inquisitorial Ordos". 6th Edition. digital