Which Bts members would be categorized as Tenor, Bass, Baritone, or CounterTenor

All of them could qualify, but if you're only talking about the most out of the Vocal line it would be Taehyung

From what I've heard from their music and read when researching:

Vocal line: Jimin, Jin and Jungkook are tenors. Taehyung is a baritone.

Rap line: though they rarely "sing", we could say RM is a baritone also ... Hoseok a tenor ... Yoongi is difficult, I would say bass, based only on personal perception.

Hope this was useful. Have a nice day!