Half the flock has been ill, one after another

[Ccort]

One hen died, don't know why. I've created other threads, desperate for help. She did have thrust and kidneys ended up being in horribly shape, died quickly. Another hen has crop issues. This hen DID have long standing crop issues, survived, crop issue resolved but doing a lot of THIS. Standing still, often head down. She has just a few feathers coming in around her face. Obviously, something is wrong with the whole flock. Vet is little to no help and mostly unavailable.
Treat with Tylosin? Something else?
They've been given Safeguard. Yes, she's eating and drinking. Age 3.5.