What is the most logical next event?

How to referee two irritable cats that don't get along
Desex your cats.
This is especially important to control the behavior of male cats. Neutered male cats tend to have less problems with aggression and spraying, which is a sign of being territorial.
Desexing your cats will not always solve the problem. However, without the hormones that cause the sex drive, castrated male cats are less likely to get in conflict with other males and harass females.