I can't tell those black haired guys apart.

And the two guys with short blond hair are just as bad.

i kinda can. one has shorter black hair (Haru), the other has longer black hair (don't know his name), then the lighter hair ones, the teacher guy has really short hair while Natsu is longer. think of it as, long dark hair dude is the seme for the short light haired dude. the Haru and Natsu unknown.

I get confused too

I was using the goatee to tell them apart

Bingo, you nailed it! :^)