Hi again, Ann.
I'm glad that you used the scent transfer method to help get each cats' scent on the others, to help with the transition of the new boys becoming part of your feline household.
I hope that you have also tried the Feliway calming pheromone plug in or collars for all the cats. Here is more information:
In addition, you can offer the cats some Rescue Remedy for Pets in their water, which is an over the counter homeopathic calming remedy. Make sure it's the formulation for PETS, as there's one for humans, which contains alcohol, and you don't want to give that to them. Here is more information:
You can also use Composure treats, but don't use the Rescue Remedy and Composure treats concurrently; only choose one to give them:
Hello, Christine and welcome!
I'm sorry you're experiencing this problem with 2 of your kitties. Bless you for rescuing; you literally saved their lives!
I'm so sorry that this aggressiveness from the 4 year old caused your oldest cat to sprain her leg. At her age, it's important that she's not injured, nor stressed.
I have several suggestions for you, that will help restore harmony within your feline household. First, get some Feliway Multi-Cat plug in pheromone diffusers. These resemble plug in air fresheners, but have no scent to humans. They are available in major pet supply stores or can be ordered online. These contain a calming pheromone, that should help with some of the stress/anxiety in all the cats at this time. Here is more information:
The same type of calming pheromone comes in these two collars, so you might want to put one on each cat:
There are two other over the counter oral calming remedies which might help: Rescue Remedy for Pets (there is a human formulation which contains alcohol, so make sure you get the one for pets), which you can put in their water (follow directions on the package) and Composure Treats. Don't use these concurrently; just choose one.
Have you tried to enrich the cats' environment with one or two tall cat trees or kitty condos, if you don't already have one, and some great toys they can play with by themselves and/or with you. There are interactive toys, too, like a laser pointer and feather wand (don't leave the feather wand alone with them, as pieces can be chewed off). Here is a great list of toys you might want to try, including a cat dvd, which they will love! I had mentioned these in the past, but will add them again, for you, here:
(if the links don't come out blue and 'clickable', just copy and enter them into your browser).
If nothing else works, I always leave prescription medication as a last resort. There are many in this class, that will help Sissie and the one male who is aggressive feel more relaxed. You can read more about these below, and discuss them with your vet, if necessary:
I realize your cat isn't spraying urine, but scroll down about halfway on this page and click on each blue link for a medication that helps with aggression, then discuss which one may be best, ***** ***** vet.
This is a process that takes a while. The cats have to establish a 'pecking' order. If you have a baby gate that is too short and they can jump over it, try to get a full sized mesh one, that is too high to jump over, so they can see each other, but Sissie won't be chased. Here is an example:
I hope things will begin to improve, soon and keep them separated as long as Sissie is still being chased. That's not fair to her and I'm glad you're intervening to help her feel comforted!
I wish you a wonderful Holiday Season!