You just need to read which one is about to kick something off and correct them sternly for considering indulging in that behavior.
I agree--You need correction BEFORE it escalates. Watch body language, watch the eyes and ears, and step in between them when you see it the signs, facing the guilty one, BEFORE it escalates. Step into him, if necessary. Stop the feeding preparation until he is calm again. Be persistent with this.
Do they have a good sit-stay? If so, put them on a sit-stay, and if one moves, stop the feeding process, make them sit and stay, then continue. Put a leash or a short 'handle' on him if necessary.
I have 2 rescue GSDs, and the female is VERY dog aggressive. She has been here about 8 weeks now, and they now are eating peacefully right next to each other. But, I don't leave them alone until they are finished and then the bowls are put away. There have been other issues, but I don't let her get away with aggression in any of those situations, either (toys, who gets which bed or crate, etc.). Actually, once she got the rules down during feeding, she improved in other areas, too.