Don't they know about your allergy? Of course they should have cleaned the house if they knew it would bother you!
They lock the cat out of the living room & kitchen for me.
I remember once babysitting my godson. He was playing on his playstation in the games room and asked me to join him and watch him play (ever since he played a zombie game on that playstation, he's a bit afraid to go to that room alone when it's dark outside
The cat had been sitting on that chair and the cat's hair was triggering an astma attack so I told the boy that I'm sorry but I couldn't sit in the room due to my cat allergy.
The boy said: "no no no...clean...me clean for you"
After which he started to clean the sofa thoroughly and he said that he would come and get me when it was safe to come back.
I'll just have to avoid the sofa in their tv room.