Update in case someone encounters the same issue and look it up as I did for my quails:
- Neck wound healed nicely and did not occured
- I found another vet that knew well about quails, his assistant is also a breeder.
They all had a respiratory infection. They had amoxicillin but developed a resistance to it. Now they are being treated with another antibiotic called " pneumobiotique". After just a few days their eyes got back to normal with that antibiotic. They are more active too so I am quite optimistic.
- Came out they also had roundworms although they've been treated last month. They must have been very badly infected when I got them.
- The vet treated them with a spot-on for parasites and mites. Considering how they act after he applied it, he thinks they also had an issue with that