Thanks for the extra information. The fact that all the cats are doing the same thing makes me think that this is likely infectious. The best thing to do is to take the cats to a vet to have an ear exam performed with an otoscope and ear swab and microscopic exam performed. This exam and test will tell you what is causing the symptoms and will enable a vet to tell you what medication will be safe and effective.
Ointments with similar ingredients to the one that your doctor prescribed to you have been used in cats, but it is important NOT to apply any medication without having a vet exam performed first. the reason for this is that some normally safe ingredients can cause damage to the ear drum and inner if the ear drum has already been affected by the disease process that is causing the shaking and scratching.
Ultimately I realize that it would be nice to be able to use something that you have on hand at home but I do not recommend you use the ointment until your cat is examined by a vet, it would be an even bigger problem if the medication causes more damage. On the bright side...hopefully the local vet after examining your cats ears will approve the use of the ointment that you already have, so you can avoid buying more medication from the vet.
Please let me know if you have any follow up questions. I wish you the best of luck.
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