Fear Aggression between house cats?

Question
I have two Siamese cats, George and effie, we got our cats as kittens and they are both 5 years old. They have been best of buds until a 1 1/2 months ago. They are both declawed and fixed. They are traveling cats, cars, camping, and even go on bike rides together. The boy cat has always been laid back and the little girl is playful but likes to hiss. The hissing has never been a problem b/c it was never an aggressive hiss. My husband is in the navy and we move allot. We moved to a new house about 4 months ago. They both love to go outside but since they are both declawed, me or my husband always go into our fence back yard with them. One day, 1 1/2 months ago, they have changed. My husband was in the back yard with them. He was sitting on the deck petting the girl cat (Effie) and the boy (George) was in the corner of the yard eating grass when all of the sudden a cat jumped the fence and came after George. My husband ran inbetween them before they could come in contact with each other. George took off running back to the house and poor Effie was scared sitting there and George wanted to attack her. It took hours for George to clam down and we locked Effie into the bedroom for a few days. I should tell you that Effie was so afraid of George that she peed and pooped in our bed under the covers. After the 5 days of being separated, they were fine back to normal loving and play again. Then about one month after the first time, George was playing in a suitcase on the bed and Effie jumped up there, I guess she was shocked he was there or something and started hissing and snarling at him and George snapped and when in to the aggressive attack mode again towards her. We split them up again but this time they are not going back to normal. Well, I should say Effie is not normal. She acts so fearful of him and gets defensive toward him most of the time by hissing, snarling, and getting low to the ground. Then about once a day they running and play together and once in a while they will sleep together in bed. When she acts like this Georges ears turn back and his tail get big and this hair stands on end but we quickly split them in fear that George will get out of control again. How do I stop this behavior? I can't get her to stop hissing at him. They are both so on edge all the time every noise that they hear puts them on edge. I bought some stuff called good kitty to calm them but they just sleep more and when they awake it is back to the tension in the air. We are so stressed out over this and are fearful that we may have to get rid of one of them. I just need this house to go back to normal. Please Help!

Answer
Hi Julie!
Obviously, the cats were traumatized when the strange cat tried to attack them.  Also, cats do NOT like change, and it probably doesn't help much that you move a lot, although I realize that cannot be helped.  I certainly do not claim to be an animal behaviorist and someone with that ability may tell you different.  I can only tell you what I would do.  I would not separate them.  I feel like when you do this, it is only making it worse, as they both have to get used to each other all over again.  It's like rewarding bad behavior.  I think I would leave them be and just see what happens.  I know Effie especially seems frightened,and I know this can be harder on her, but when George starts his aggression, maybe you could hold her and comfort her, while telling him NO sharply.  Don't every spank or hit your cats, as that does not work with cats.  They do not respond to that at all.  You may want to keep a squirt bottle filled with water and use that to spray at George if he gets too aggressive.  I really feel that if you just let it play out that eventually they will be buddies again.  I know in my own cats, sometimes one will get a little rough and there is some hissing and even crying out, but it is only for a moment and it passes.  Please let me know how it works out for you.  Good luck and God bless.
Becky