Hallo,

I have played teh game just once, but we had a problem using the fighting cards.

When someone uses a aks, which fighting caeds counts.

every melee card or only melee cards and sharp melee cards of only sharp melee cards

by the monstersdo you only use the barriercard only if there is a barier.

does this also wordks for hidden investigators cards?

If I've understood it correctly it works like this:

If you have a sharp melee weapon you use the first card saying either "melee weapon" or "sharp melee weapon". The "sharp" or "blunt" parts just give you more cards that you can use, depending on what weapon type you are using.

The monster vs barrier are only used if the monsters try to force a barrier, otherwise a new card is drawn. Same goes for monster vs hiding, they are only used on hiding investigators.
The reverse is also true, if a monster is declared to attack a barrier, you should draw untill a monster vs barrier card comes up.