Chickens not eating, beginning to die

[Eggspectation79]

I am in a panic. One of my Red Ranger hens (5 months old), just got sour crop again. First time we treated at home successfully. This time I had to take her to the vet. He treated her there and sent me home with meds. 2 hours after getting home she had a seizure and died. Then the next day, a different Red Ranger (5 months) began panting heavily. I spoke to the same vet and he said it sounded like a respiratory infection and to treat with Tylan 50 subcutaneously. She was about to start her second day on Tylan 50 but just had a seizure and died this morning. Now my Bantam rooster is lethargic and not eating much. He is separated and inside my house. Rest of the flock seems ok. None of the deaths seem related but I'm afraid my rooster may now die. Any suggestions???