I can assume the BBBB can be divided into Baritone I & II and Bass 1 & II, but what about tenors (assuming they’re all tenors and not countertenors)? Is there another name or does it go from Tenor I to Tenor IV?
I could be wrong, but I believe that "B" specifically refers to basses; to reference the baritones in the "instrumentation", traditionally you would use "Ba". Therefore, according to the instrumentation you provided, the song is for Bass I-IV and for Tenor I-IV, and you leave it at that. To include two separate baritone parts, two separate bass parts, and four separate tenor parts, you would say "TTTTBaBaBB".