"The final two months" was marked incorrect. As far I know, this is correct...?
Yes, I'm pretty sure. It probably just wanted last, rather than final, even though they're synonyms.
I don't think they're synonyms in this case. Last refers to the two most recent moths, while final refers to the end of some time period.
I can't tell if this is looking for the two months preceding the current time or the last two months of the year, or if it's sort of ambiguous in isolation like it is in English. I assume final months?
Why is los used in this sentence? Could les be used instead, and if not, why?