Badger,when I first got Vinnie,I just about had a nervous breakdown,cried rivers...I could not handle the way Rocky and Chico behaved towards Vinnie.
I was a nervous wreck! I even called someone to pick up Vinnie(the friends who found him)but in the morning I looked into his sweet little face and I just could not do that to him......
Your situation is different,Simon is a grown cat,a very pretty one too....and cat-fights are awful,Rocky and Chico had a cat-fight outside yesterday,a quick reaction with the water hose stopped it
I honestly believe things will get better once Simon is neutered and for now,equip yourself with a large water spray-bottle! NEVER break up a fight with your hands,but I suppose you know that....