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Cats are prone to respiratory illness and it sounds like your kitties have passed it to one another.
If the mucus from the nose stays clear, you can wait it out. Try to make sure they are drinking ok because cats can get dehydrated easily. If the mucus changes color, you will need to see a vet for antibiotics.
The color changes are normal when a runny nose is present.
Let me know if you have more questions.
Your vet would have to prescribe the antibiotics. They cannot be gotten without a prescription.
Something that you CAN do at home is use pediatric saline nasal drops in the nose to help clear the congestion and make breathing easier. You can get them at your local drug store.