Cat Allergies...

My wife and I have just entered the world of Foster Care, officially having a group of 3 kids turned over to us recently. We've had them in our home several times prior. The oldest has allergies to cats, that manifest themself through asthma. My wife and I have been trying to come up with a solution to the cat allergies, as we had two cats, one my wife brought with us into our marriage, and a second we got about a year ago. A little over a week ago, we found a new home for the cats, and have been hoping that the oldest would have fewer allergy problems after. This was after we tried medicine, an air purification system, keeping the cats out of his room, airing out the house for several days, etc. After we found the cats a new home, we deep cleaned our house a few times, steam cleaning the carpets, furniture, etc, all trying to help him out. Well, it's happened now, and he's still having problems. I should say he is 11 years old, has been away from his parents for over a year, and I don't think he's particularly happy to be with us. I suspect that he exaggerates his problems with our home as a result. Still, he definitely does have cat allergies. I'm wondering if anyone out there has any suggestions about two issues. First of all, and most importantly, do you have any ideas as to what we can do to help him have fewer problems with allergies? Secondly, what can we do when he refuses to try new ideas, and states that the only thing he can do is to get away from our house, that we hate him, his CPS worker, etc? Thanks for your help!