I believe that you will have to contact AF concerning how many carryon pets are allowed in a cabin as there is nothing mentioned on their site. BTW, their site says the weight limit for the pet is 4kg including the bag. 4 kg = 8.81849 lb (8 lb and 13.0958 oz) That restriction if they enforce it really limits you to the type of pet you are traveling with.

BTW, in NYC there are rats running around that weigh more than this.