Sorry your parents had this experience.
I'm not sure if you are going to get any more recourse than you have.
Technically speaking there was nothing wrong with the property - but it sounds like of neighbours/surrounding area?
Did you book a superhost or someone with a low rating? Or with good reviews to ensure it was peaceful and quiet for your parents?
You can rate the property lowly for being noisy outside and disturbances, but I don't think airbnb will refund you the full amount. I would be surprised even if you did have video, but then again airbnb does usually favour guests over hosts.
It's why I never book long stays especially if its a new property I've never stayed at.
A few lessons learnt I suspect for you
All the best
MK