I have the exact same issue. Get a good dog behaviorist and be ready to put in some work. It’s been two years and it hasn’t gotten much better. My two girls can’t be in the same room together. They have to be crated and rotated throughout the day. It’s a pain, both logistically and emotionally. I really hope your situation gets resolved and they can be together safely again but if it doesn’t improve, I’m not saying you have to, but keep an open mind about re-homing one of them. It kills me to have to fence them off and split my time between them. And the panic I have when I think I left a gate or crate open feels like it takes a few minutes off my life. I’m at the point where it feels like they both may have a happier life apart.