I just played this and initially failed, having underestimated the nekkers. I then sought salvation in different kinds of bombs, of which, dancing star made things really easy.
Dancing star, you see, creates a fire, which keeps burning for a while after the explosion. Before the creatures reached me, I made sure to thrown a dancing star in front of the bulk of them and quickly finished the front straggler. Now, the fire kept the beasts back and damaged them steadily, so retreating upwards toward the entrance and using about two more bombs made things really comfortable.
In the cave I didn't know yet, but later, while fetching the ostmurk, I encountered a similar situation. There I confirmed the amazing power of axii, turning the first attacker to your side for a short (but substantial) while. The key is to keep the button pressed until the opponent is turned. He will the shine in white light. So, make sure to start casting early enough!
It appears, there are no special oils, so I would recommend whetstones or generic oils, such as Falkas Blood.