Would love to get your advice

Hello cat lovers (:
I'm new here and just joined.
I have 3 lovely cats that I love so much.
They are 10 and 11 years old. One girl and two boys.
They are indoor cats and grew up together in harmony.
3 months ago a cat from outside enter through the window into my home and there was a big fight. Since then,
. my cats became post traumatic and are afraid of each other . They attack each other as if they are strangers and are terified and shout and hit eachother
. I used a paw gel - Pet Ease of Nutrivet for 3 months.
It helped for a while but now became worse.

I heared about St' John's wort for enxiety and stress however the veterinarians I tried to consult here in my country (Israel) haven't got much experience with this hurb on cats and before I try this hurb I'd appreciate your kind advice about dosage and for how long to use it.
.I can get st' John's wort of Solgar only.
.
If anyone has an experience with this hurb, please share.
Thank you !
Melania

Maybe this info will help. What you're describing is displaced, or redirected aggression. Ideally you should seperate them and try and re-introduce them. Make sure they associate good with each other, to play with them together, feed them together, give them treats together, so they no longer associate bad with each other. 

http://jacksongalaxy.com/blog/2014/08/21/aggression-in-cats

Hello Missmims,
Thank you for your advice and for the interesting article !
My cats attacked eachother out of fear and panic. They aren't aggressive; they are defensive and simply became confused and I try to relax them so that they remember that they're very good friends.
I do separate them and try my best to calm them.