At beginning there might be explanation that if diseased disease will drain all of your skills and do not seem to hit always hitpoints (they do hit hitpoints too). After a while disease will go away itself if not cured.

 

Between 10 and 11 there should be clarification to take brutal arrows and / or runes for crumble undead spell.

Personally I tried melee which hit low, then I tried Comp ogre bow with Adamant brutal which hit bit more then melee and eventually I used crumble undead spell with chaos gauntlets that seemed to hit the most of them all.

 

 

This seems only quest that did not had "Quest complete" screen, simply gained experience and had info in chatlog below saying Quest complete. Might been because I was diseased at that point but rather seems to be a bug. Just incase did a report to RuneScape.

I've edited the guide with a warning about disease. The guide already had a sentence regarding crumble undead and brutal arrows, so I've left it as such. Thanks so much for your help! :)