Sounds like the dominant dog has gone...to the Rainbow Bridge...and the position of dominant status is now open. And there's 2 contenders for the title. My thoughts...and I'm no expert...would be to acknowledge one as dominant & encourage it with things like feeding it first. I'd look for the one that seems to be backing down most in these fights....that is, falling into a lying position (i.e. submissive pose). That's NOT the dominant one. But when there's danger of them hurting each other while this dominance balance is being worked out, I'd check it out with an animal training expert. Maybe your vet knows somebody.