Zippy - It's likely the "D" that makes you shake - the decongestant. If you have allergies, as opposed to sinus congestion (which is not always caused by allergies) you may be able to do without it. You might see how you do on just an antihistamine.

Aguu - You can and usually will develope a desensitization to your own cats - it's the process that allergies shots are based on.

Purrley - this could be why your daughter is bothered by your cats and not hers, but it could also be sheer numbers like you suspect. Every allergic person has a certain tolerance level for any given allergen - a little bit may not bother them, whereas a lot probably will.