I agree that a diet change for the IBD kitty should be your primary treatment plan. A grain-free canned food or even better, a raw diet, are the best options. What does she eat now? What are her symtpoms (diarrhea, vomiting, both?). You might be interested in reading some more info here:
http://www.catnutrition.org/ibd.php
As for the asthmatic, please read this website for some up-to-date info on treating with an Aerokat asthma inhaler:
http://www.fritzthebrave.com/
Like Love4himies said, long term prednisone is never desirable unless there are no other options. I know many a cat that became diabetic from pred.