hissing/peeing

Question
Hello,
I have two questions.  First, I just got my female cat spayed yesterday.  When we got her home, her brother (blood brother, we have had both since birth) started hissing at her, and has continued to hiss and will not stop.  He even started hissing at me when I was near her.  She was around a lot of cats, as it was a mobile spay unit and a girl at work suggested that this may be the case since she may smell differently.  Could this be it?  Any suggestions?
My second question has to do with cats peeing.  The male is neutered and now the female is spayed.  They use their litter box all the time.  However, one of them has peed on the spare bed twice already.  And today when I got home, one of them had peed and pooped on the table cloth (which was folded up on the table).  Any idea why this may be happening.  Thank you so much for you time.

Answer
Well cats are creatures of habit and they don't like change of any kind
my guess is that they sense disorder in the house... your female cat coming home and like you say they smell the other animals on her..they may smell the surgical site or change in hormones.. animals can smell a lot better than we can   They are really stressed and upset
I'm hoping that once the female cat is all healed, that they will go back to their normal routine.  Try to keep their lives very habitual and structured.. Make sure you buy a good product that will clean where they urinate and totally remove the smell because once one of them starts to pee in an area, they all will (if not cleaned)  Feliway plug ins seem to have a 50/50 success rate..they are expensive but worth the try if you have the money  one or two should be enough for the whole house if you keep them centered.  HOw about catnip? Buy the more expensive kind my cat is immune to the cheap stuff. Try to think if there is anything you are doing differently with their routine after the cat came back home then before she left... are you giving her most of the attention, etc... try not to be too obvious...anxious.. about favoring the recovering kitty. Just keep an eye on her, give her the meds, treat her as if everything is the same ol' same ol' routine.....thats the way she wants it, and the other cats too