Student or Learner
My question is: 'arenít they?' is OK here?
Hmm. I didn't notice it was "wrong" because there is no single-person, either-sex word.
But it would perhaps be better in this case to go with all plurals: All the inhabitants ..., aren't they?
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.