Why is it fhir for man here when fir means men and fear means man.??
A complete rundown can be found here.
Because this is the genitive. It changes based on the meaning.
Why does fhir and fir seem interchangeable in this lesson???
Can this be literally "Hat of the man"?
It could be "the hat of the man". The genitive definite article makes both of the nouns definite.