Jeslyn fight 🤦🤦🤦

So this is my first run on pathfinder and yeah I'm a noob basically.

Now I've harrived a the Grey garrison assault, and despite I've met some hardship, I was able to overcome them all. Buuuuuut, this jeslyn fight seems different. My party gets wiped out in few minutes and it's barely capable of land some real damage to the enemies.

So what do I do wrong? I know that my party isnt well equipped nor" well trained ", but this time I don't know what to do.

My question is, if this fight is doable for a noob (even without the crusade), and B) this fight is mandatory?

I really liked this game, but I don't wanna restart the game in all honesty.

Edit : So I've beat the fight in the only way I thought I could beat so, I've just low the enemy damage to 0.2 (yeah I feel dirty as shit). The only positives it's that I thought that damage was set to a normal standard, while it was set on 1.5 damage. Maybe this is also was the reasons enemy kick my ass so often Idk.