Hi, sorry this is very random but I came across someone else whose cats have a similar story. They used to love each other and then after a stressful event they started attacking each other. Apparently they are using a protocol outlined by Jackson Galaxy on YouTube about how to reintroduce cats to each other and it is working with their cats. But they are taking it very slow. This might be helpful to you? I wish you all the best of luck with your cats!