When interrogating the peasant couple after finding the body. Telling them you don't believe them and starting combat results in them having no health bar. They are unkillable. Even after stunning them with Aard and executing them, the still register as alive, and continue to combat bark.

There is no way to resolve the quest using this option.

I had the same problem just now, solved it by using the fast travel away from there then back, and when i got back they had health.

All you have to do is to get out of the combat ( run out from the villige about 80-120 feets away) then meditate 1 hour and back to kill them.

Tried a variety of suggestions here but what finally works for me was to escape combat and go about 1km away, a few hundred feet was not enough. I suppose fast traveling to another location should also be sufficient though. Then meditate for several hours, followed by a save and reload. Not sure all these steps were required but with this combination I was finally able to kill those SoB's and get this quest cleared. Currently on the latest patch 1.31.

i've never been able to find the body- could someone tell me where please? i search the huts and find the one full of blood but have never come across the body. i've always felt there was something more to this quest

Use your witcher sense around the outside of the house. You're looking for somewhere a body/bodies could be stashed.

thanks, will try next playthrough