I would personally use Tenor I through IV; there are some style- or technique-based names (think Lyric vs Dramatic), but unless you call for those specific voice types, you can safely name them as Tenors.
The same can actually be said about your Basses too - you don't necessarily need to have two Basses and two Baritones, unless you have need for very specific ranges.
I would also recommend checking out Composing for Voice by Paul Barker - it's an absolute goldmine of information about writing for voice and different ensembles and voice types. Plus, it's a fun book to read (if you enjoy composition and technique discussions)!
I hope this helps! Please feel free to add a comment if you would like more information or would like to clarify anything.