I have two cats that have lived with me for 6 years, and a third that has been with me for 2 years, all were kittens when I got them, and they each adjusted to each other well enough. A couple of months ago, I took in 2 more adult cats, who are also 6 years old, and have lived together their whole lives.
The two new cats are ganging up to bully the youngest cat, threatening and chasing her away from the food and litter boxes. The young cat will then run away, and I have to call her for a couple days to get her to come back. When she comes back, I separate the new cats to keep them away from her, but she is scared and agitated for a day or two before calming down, and it seems like this situation is starting to drive her feral.
I am looking at ways I can keep them permanently separated, but I feel that this isn't an ideal solution.
What are some ways I can discourage the bullying, and help the younger cat feel more secure and that she belongs at home?