Hi, this is Doctor H and I would be happy to assist you.
What have you tried so far in order to curb the male
As I said in my previous mail, I tried pheromones, hissing at the agressive cat and chasing it off out of the cat flap or outside of the room where he attacked the other cat. I am now going to buy an extra cat tree to put in another room (I have one at present), However, the agressive cat seems to attack the placid cat, even if she is on the cat tree. The placid cat (female called Amber) now sleeps in my bedroom, which I feel is making her feel secure. However, in the morning, she is scared to get downstairs, as she will most probably be greeted by agression.
Okay, how many litter boxes and feeding stations in all?
It sounds like you've researched cat aggression a fair amount!
I'm sorry, I didn't realize that the garden was being used for that purpose. Kindly, may you describe the layout of your household as well as where each animal spends the majority of his or her time?
its a house with bedrooms and bathroom upstairs. Sometimes one of the cats sleeps on the landing. My female cat used to sleep on the landing waiting for me every morning. But she cannot do this now, as the 2 boys will chase her away. One of the male cats is agressive, and the other one just chases her away without attacking. Downstairs is open plan except for my painting studio which has a door. The open plan has a living room extended into a conservatory which can be closed by a sliding door. However, there is no cat flap there, so I can't keep some cats in there. It is open plan to the kitchen where the cat flap is. During the day, the 2 males will sleep in the sitting room or conservatory, whilst my female cat sleeps on a chair in the hallway, or hides underneath a sideboard in the living room. Occasionally she is perched on a scratching post in the conservatory. Wherever she is, the agressive cat will have a go at her at least once during the day.
So the best thing to do is to allow Amber and Cuddles to have their own spaces in your household.
For Amber, it sounds like the best thing to do is to allow her to maintain her territory in your upstairs area among the bedrooms and bathrooms. This will entail allowing her a feeding station and and two litter boxes with unscented, clay based litter.
The reason I am recommending this is to allow her to stay in the upstairs area, away from the two other cats. Otherwise to get to the feeding station she has to go downstairs and risk being attacked by one of them.
The same with going to the garden.
Additionally, it would not be a bad idea to have bloodwork done on the primary aggressor - with 11 year olds we can start seeing kidney and/or thyroid disease, which if diagnosed and treated could improve the behavior.
In the meantime, there's some really good information here: https://vet.osu.edu/assets/pdf/hospital/behavior/evironmentalEnrichmentForIndoorCats.pdf. You can see if implementing these tactics allows the males to calm down in the lower living area.
Please let me know if you have any follow up questions.