Day 7 of Addie hissing at George

George was neutered last thursday, so this makes the 7th day he has been kept separate from Addie, his sister, because she's hissing. This means both our bedrooms are occupied because neither kitten can be out with the dog and 2 other cats unless supervised at all times.

We've done everything, from swapping rooms, to vanilla extract, to rubbing a towel on both. Nothing works, except it seems to be taking Addie a little longer to decide to hiss. Usually it's a sniff at the incision site that starts her going. I've routinely checked the site, there's no discharge, he doesn't seem to be in pain from it (I can touch the site and he doesn't flinch or cringe....he tries to pull away, but it's more of a "hey, pet my head, pet my belly, I'm not comfortable with you poking my private area!" type thing, not where he seems to be hurting). It's only puffy in the way any neutered kitty scrotum is....just a bit of fuzz over a soft, empty pouch that slightly stands out, nothing I'd consider swelling.

So, what do you guys think? I'm gonna give my vet a call, just to be on the safe side, but with no sign of infection and George behaving normally, all good on the eating, drinking, litterbox fronts, I don't think anything is going on with George. Addie, I should mention, is a MOUTHPIECE and never shuts up, so it might be all her.
Any ideas?

I would watch his behavior, if he seems lethargic, take him in, it could be infection. As far as she is concerned, it will take some time, he smells different now and it will take a bit longer for healing to complete

The more you change their routine (separation, etc) the longer it's all going to take. So she's hissing... big deal. Get them back to their routine (and each other) under your supervision - but just be there for true fights that get out of control (have a glass of water handy if necessary) and might actually hurt someone, but otherwise let them be. They're upset because of changes and won't get back til they're allowed to work through it and relax again.

My little girl cat always hisses at my boy when he goes to the vet including to be neutered. It usually only lasts two or three days and I only put them in separate rooms when I am not at home, other than that I give them both full run of the house. It sounds like you are like me, it gets on your nerves and even seems a little scary when one starts hissing at the other one but it is part of cat behavior. My boy cat doesn't hiss at the girl when she comes back from the vet and one of the vet techs where I take them told me that she thought the girls were more prone to hissing at different smells.