Calico cats being aggressive

Question
We have two feral calico sisters that just turned 3 years old. We have had them since they were kittens and domesticated them.  They are both fixed & front declawed (indoor cats only).  All of a sudden 2 weeks ago they have been aggressive toward each other.  Nothing has changed in the household..  The first Calico will chase and slap her sister in the face.  The second will not back down and growl and hiss until her sister walks away.  We have tried putting corn starch on them and have had Feliway diffuser plugged in since last week.  They seem to have calmed down a little but are still having spats. We sleep with one cat in our bedroom at night and close the door and leave the other more aggressive cat to roam the condo.   I know Calico's are notorius to be like a Hershey bar with almonds, half sweet and half nuts but we are hoping the bad behavior will stop soon and they will get along again.. Any suggestions?

Answer
Sometimes aggression can be caused later in life by declawing.  It's the second most common complaint of declawed cat owners, following litter box problems.  There's rarely anything to do about that, so hopefully, that's not the problem.

You should consult a vet in case this aggression has been caused by some type of physical pain, like bad teeth, ear infections or urinary tract infections, etc.  A cat who feels badly often lashes out aggressively.

Could be something happened while the cats were in the room together that scared the aggressor.  A clap of thunder, a siren going by, a dish breaking, or seeing a strange cat outside the window can all cause redirected aggression.

Fortunately, time heals most wounds and cats make up on their own.  It would probably be a good idea to separate them completely for several days so they can both calm down.  Right now, they're just reinforcing each other's behavior.  Each spat is likely to worsen the situation.  I'd see about reintroducing them in a week or so.

In extreme cases that just won't get better, an antidepressant might be warranted.  I've used them in a few of my cats, one for aggression.  He's on amitriptyline (Elavil), and it works great for him.  Clomicalm is another choice especially good for aggression.  Most treatments can be discontinued after a couple of months, once the behavior has been corrected.