<human>: Can you give me a shortened version of the text?

Hey, I've been through the internet and back and I can't really find an explanation to why my 2 cats are fighting. 

They're 4 going on 5 years old, been together since birth (brothers), they're neutered since before they turned 1 and they've gotten along pretty well until now. Although one has always been more dominant.

It started about 2 months ago, when they suddenly couldn't stand the sight of eachother, hissing and growling and fighting. We thought they where under some kind of stress so we put up more scratching posts, added another water bowl and another litter box, plus we bought feliway. After a couple of weeks they seemed to be friends again, until today...

When they're friends they can play pretty hard, when they started to not get along.... well lets just say they _fought_ instead of played hard... You could tell from the sounds that it wasn't fun. 
But today it was even worse, the dominant cat seems to be trying to end his brother. I have always been able to separate them by voice or by hand, this time i had to use a large cushion to separate them. I've kept them separated since, tried to do a meet and greet but it ended in another huge fight so they're separated again.

Well this turned out to be a long post.
<bot>: How can I help my cats become friends again, or should I give one of them away? Grateful for any hints or tips.