I didn’t read every reponse yet but had to comment as the few I read seemed to suggest this was a hopeless situation-
I don’t think so, if OP has had them from puppy-hood and is committed to being creative & persistence with prevention & problem solving, all can become a happy pack at some point.
I had a similar problem when my two Caucasian Ovcharka’s were 6 mos & 1.5 yrs for about 6 months.
Think two giant breed apex of the aggression scale behmoths staging a full blown wolf fight in the living room! :eek: My friend refers to it as the “clash of the titans”.
If I have dog savvy company, each one grabbed a tail, backed away, and secured each dog someplace else until they could chill out (never took more than 10 mins for my dogs to forget they ever did anything but love each other again).
When I was alone, I devised a system as such: glass of water (or whatever beverage I happened to be holding lol - dumped some good beer & wine on the floor during this stage, durn dogs!) splashed in their faces caused a hesitation, hooked one up to the ever present chain bolted to my living room wall, dragged the other over to her crate. Leave for 10 minutes, wala, happy dogs again.
So I had my emergency fight breakup technique down, next it was up to finding & preventing the triggers. I think this is going to be different for each pair of dogs. For mine, it was, 1) control food (no food when we are together) 2) visitors - if I have company I only have one or the other loose - I’ve found otherwise they will find an excuse to become jealous of my or the visitor’s attention 3) get everyone plenty of daily exercise.
Once I had all 3 prevention steps down, I haven’t had anymore fights. I also think it was a growing stage thing - now they are 2 & 3.5 yrs old, seem to be mellowing out.
Yes this means to some degree I’ve rearranged my life to accomodate my dogs -
But it sounded to me like the OP is the type willing to do this too, rather than give up on one or both!
One caveat, my dogs fights never resulted in blood - they were just a lot of noise & posturing. Scary as h*ll but they obviously could have done each other damage and did not. If a pair of dogs are constantly, intentionally tearing each other up, I’d say that’s a different deal maybe requiring more permanent separation.
Good luck with your pack!