Debbie,
I was a cat breeder for roughly 17 years and recently got out of the cat
breeding.  During this time the only things I've heard cats be allergic to
are incest bites and food items.  However it sounds like to me that you
are at the beginnings of an upper respiratory about to invade your house.
I would take the one exhibiting the worse/most symptoms to the vet and let
her/him know that you need enough to medicate the rest of the colony.  I
would do this as soon as possible to avoid them from becoming any sicker
than they have to.  Good luck.  I have been there.
 
Sincerely,
JUDI MAY
[Posted in FML issue 3613]