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Ringworm usually is not the problem. It causes skin irritation and rashes but usually not death.
Because of the green drainage, it sounds more like your cats had respiratory infections. They can be deadly.
There are so many things that can affect these little guys. Even fleas can kill them.
This is a good time to have mom spayed if you have not done so already. Otherwise, she will be pregnant again in about 4 weeks.
Let me know if you still have questions.
Keep in mind that different antibiotics work for different things. Even if they were on an antibiotic, it might not have been the right one for THIS condition.
Please let me know if you still need more help.
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