"Oversight officers" is good. (I'd avoid "overseer," because of the U.S. antebellum southern-plantation overtones.) Consider too "members of the oversight (sub)committee." -- "Vocal" is also sometimes rendered as "senior voting member," with the implication of added responsibility. -- As for "fiscal" (which in Spanish is usually "auditor" or "supervisor," and sometimes "inspector" or "examiner") ,"monitor" is fine. But there is a fine old English word that survives in formal business parlance: "scrutineer." You often find them observing consequential proceedings, often in meetings at which shares are voted (where they're usually in the company of one or two tellers, who do the actual counting). -- Hope this helps!