Siamese cat problems

Question
When my Siamese kitten showed up at my door, I had two cats already that were 7 years old.  They are both males, found 1 week apart and adored each other.  She was a stray about 4 mos. old and starved to death.  She got along fine with both cats and my dog for about 6 mos. Then she started attacking my gray cat.  When she went after the gray cat my black cat would join in.  Finally I separated my Gray cat(male) from the Siamese.  My other cat was fine going in between both halves of the house and got along with both cats as long as they were separate.  Now another year has passed and she is attacking my black cat(male also).  She will not allow him into the front of the house without attacking him.  He is scared to death and now stays in the back of the house with my gray kitty.  I don't understand it because my black cat always played with both cats just at separate times.  Is there something wrong with my Siamese, or is this common?  She is a female and weighs about a 3rd of the 2 big boys I have. The gray and black cat are both males and are both neutered.  The Siamese is a female and spayed.   I am at my wits end, I just want them all to get along.

Answer
Hi Candace.  Sorry to hear she's giving you trouble.  I know it's not a popular thing to say, and I hate to admit it myself, but Siamese do seem to be a little overrepresented when it comes to problems with dominance and territorialism.  A product I use called Feliway does help some.  I keep a plug-in diffuser in each room.  You can learn more at www.feliway.com  It's available at pet stores, online and through some vets (I think it's least expensive at amazon.com).  For now, you may want to keep them completely separated to stop the situation from worsening, and then see if they feel any better about each other after the Feliway has been working for a couple of weeks.

In my experience, Siamese do tend to calm down as they get older, but this is along the lines of over 5 years old.  Many over-aggressive and territorial cats have benefited from the use of certain antidepressant medications, and they rarely must be used for more than a few months.  One of my friends had a cat that was nearly put to sleep because she was so aggressive.  The cat was placed on Clomicalm, and within 6 weeks, she was a completely different cat.  After 5 months, the treatment was discontinued (but she continued to use the Feliway diffuser), and the aggressive behavior didn't return.  

My blue point has come to the belief that my bedroom belongs to him alone, and he is extremely aggressive toward "outsiders" in there.  However, in the rest of the house, he's more amicable.  I wonder if she's become too attached to the front of the house and needs to have it redefined as a shared space.  My only suggestion for that would be to place her in a crate several times a day and allow the other cats to enjoy the area as she looks on.  They'll be able to rub their cheeks along items to mark them as joint property.  And maybe if there's not too much complaining, they'll be able to mingle sometime.