Some fight requires more wits to solve, this is one of such example.
There are several ways to "solve" this fight.
You can ambush them, taking the initiative to attack, introducing your fighters to the fight one by one surprising them and you try to take out as many archer as possible.
Use your consumable. Invisibility potions, Mirror Image Scrolls etc.
Take high ground as fast as possible/sneak your way to the high ground.
You can also kite them and create a choke hold and plant cloud of daggers.
You can also trigger to talk to their Maddened leader and persuade it to attack their own subordinates, making the fight easier (you can kill her alone later).
Archer has penalties if your fighter standing next to them, making them likely to miss even if they shots repeatedly.
