Lots of people read these threads so accuracy is important, so others may seek treatment for the sick flock. Rather than thinking oh nothing i can do it must just be neighbors toxins.
We have different feelings on value of life . But I do understand limits in what one can do.
Sometimes it can take a lot of time before finding what is accurate in complex situations, but yes accuracy is important. My rule of thumb is always start with the simple things like what could be causing the birds sickness so I would first look at diet, drinking water, cleanliness of food and drinking bowls, the cleanliness of the aviary which I had covered early on but the issue remained. I looked into parasites as its a common problem and the birds were itching, this would naturally point to a parasite issue, so I treated them with some S76 that contains Ivermectin and is well known in the UK among bird owners that treats a wide range of bird parasite issues including worms but after treatment, there was no change and birds were still itching and dying. Its not parasites. Diatomaceous earth was also tried but had no effect.
I then did some further digging about in google. Somebody told me that worms are very common in zebra finches and that not all wormers are the same, most wormers on the market don't cover all worms and that I'd need to find a wormer that covers tape worms. As this is a common problem in zebra finches I thought it can't hurt to try it so I ordered some wormer that covers tape worms.
The next common thing is, and most credible are toxins in the air. I guess it can't hurt to find a way to test the air quality. I will look more into this later on today.
Congratulations! 
