My four all get along. Oldest is a feral cat. about 15 Yo, Two are the same age, going on 11 YO. Youngest is going on 5 or 6 YO. all declawed and neutered. The 2 eleven year olds fought the 1st week they were together, that was it. Other than a spat now and then they all get along.
I hope you find an answer to your problem.