ok prep for a bad spelling...
these cats have "terachial rhinophuminitis", I had an outbreak here of that once. it kills old, weak, and young, a FEW do recover but they die with sores in their mouths, choking on snot and blood, and it is VERY contagious. SHOOT every cat that shows even a sniffle, and bury or burn them. watch the rest of the kittys, they may not develpoe symtoms, some are immune and resistant. I advise you NOT to shoot the healthy ones, if they are there for mousing and rat catching, you do want some there. the ones that remain heathy out of this 40 will have kittens who are resistant too. I had only 2 healthy ones left out of about 13, and since I havent had another outbreak and all the cats I have are from those 2's kittens. if you see a cat with those symptom from now on and they are as you say kinda wild, shoot them, your doing them a favor, as few will recover, and they spread it to other homes and cats.
you have job on your hands and speaking of hands pitchfork the dead ones, this disease can transmit to people sometimes. (my iinfo came from 3 vets I ask at the time, so i err on the side of caution).
make a day of it, get a bonfire going that incinderates whatever you toss on the pile, and start hunting. Do it NOW, they suffer horribly sometimes, they cant eat or drink or breathe. Dont shoot the healthy ones so they pass on some resistance.
I hate whacking cats but sometimes you just gotta do what ya gotta do.