A. From your description it seems an infective upper respiratory tract disease which is affecting all of them. Primary viral and secondary bacterial infections are common.
Other possible cause ( but unlikely) is an upper respiratory toxicity.
If your cats are regularly vaccinated that should not a problem the disease could be self limiting. If you notice that the coughing and sneezing episodes are persistent and some or all of your cats are showing more signs then I would recommend to have them checked by your veterinarian. Unfortunately antibiotics may be needed.
A. Sounds like your cats got exposed either am aerosolized irritant (i.e. Smoke, sprays, chemicals) that is causing irritation of their trachea. I recommend you try and find the source and get rid of it. It has to be something you introduced in the house right before they all got sick/irritated.
If they are still coughing/sneezing and it's not improving within the next 8-12 hrs then I would schedule an appointment to see the vet for at least the most affected cats if not all of them.
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