Caught in the cross-fire?

I have three cats - Kit, Caspian and Cierron. We got Kit and Caspy together from the same litter, and Cierron 2 years later. Suddenly Cierron and Kit have started picking fights. Now he and Kit are grumpy with each other, and poor Caspy (who is the sweetest, non-fighting sort of cat) keeps getting beaten up. He has these scratches on his face and they're always chasing him around, not together but at different times. Why did they suddenly start fighting and is there anything I can do to stop them bullying Caspy?

If you dont have any other ideas you can always try with Feliway...

Probably it is some sort of fight for dominance.
Sometimes, if you cant manage it / there is no good solution, you must consider to find a new home for one of the fighters.

In the meantime, you can also try to have one of them in a own room, with perhaps a net door in.