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There is a very effective product that you can get from your vet called capstar. It works wonderfully.
What makes you think that they are allergic to prescription flea products?
This is not a common reaction, especially if you saw it in all the cats. You will see this reaction more with Hartz products (which should not be used) than with frontline or advantage.
You are correct that you should not use it if you are seeing these symptoms.
You can talk with your vet about prescription flea collars for all the cats. They are pretty strong and very effective. You can also talk with the vet about an oral medication like capstar. I think that you would be happy with the results from this.
Let me know if you still have questions.
No problem. I hope that you will accept my answer.
Glad I was able to help!