Hi , I'm James DVM MRCVS and would like to help you with your problem.
Sorry to hear about your domestic problem with your cats.
Let me start by asking ;
Do your cats go outdoors or do you like in an apartment ?
I shall start by letting you know that the ideal situation for cats is one cat per house hold .
Cats are solitary animals and like living on their own .. and so having more then one cat in a house can cause trouble.
Sorry , got cut off
Well . there are few things you might want to try first .
1. You can try and use a product called Feliway - http://www.feliway.com/uk/
this product is great in defusing tension in a multi cat house hold
It spreads natural pheromones which calm the animal down and creates a calmer atmosphere.
2. Looking two adult cats in a small house without allowing them to avoid each other is a problem . Cats must have the option to not see each other and avoid each other for long periods of time . for that end you should try and have separate feeding bowls and water bowls , located in far ends of the house. as
As well you might try and allow them to get out of the house , this will provide with the necessary outdoor environment which will help diffuse the tension between them .
If all else fails then and they are still at each others then it might be wise to give one up for the safety and happy living of both .