One thing I have found over the years is there really isnt "just out of the blue". Things have built for awhile, one dog is being a bit pushy and one is being submissive, and we sometimes as humans dont see this , we see it as like the one nipping at the other during play as "oh its just dog behaviour" . but really it isnt, it was our lack of controlling the moments that leads the dogs to believe and to think they "can" and "must" control the moments. (leading to arguments and etc.)
Can dogs live together after moments like this. Sometimes , sometimes not. But it can take some time to get things under your control. Not the dogs control.
There are behaviorists out there that are good, buyer beware tho, if they rush or tell you to strap on some device that will magically fix this, they are out in left field. RUN.
The advice earlier with the humans rule and pack mentatlity as noted is EXTREMLEY EXTREMLY DANGEROUS (inser the guy recently March 30th in Holland Michigan that was trying to break up his two dogs and fell into the fight and got very injured, the neighbors called the police, now all the dogs will probably die and the owner is very hurt).
These are terriers by nature these dogs can easily if left untrained in high stress moments can go into red zones in their mind and bite everything within reach when arguing (you, kill each other, etc etc). Its scary and it has to be understood but not feared.
Gaining control of your home is step one.
WORKING ONE DOG ONE AT A TIME ! (as my trainer taught me, you DONT have 2 dogs, you have ONE DOG 2 TIMES)
Excercise /play one at a time, toys and fun times can trigger excitablity -jealously-fighting
Give this a GOOD MONTH of one dog at a time. ONE DOG AT A TIME, allow them to see the humans have full control and have created a SAFE enviroment for them. This will lead to a dog feeling secure and lessen the idea in their mind that they "HAVE" to control their world.
Make yourself worthy of looking up to.
Use Find ME For Food - nothing in life is for free thinking. No treats or toys for being just there.
Want the toy to be thrown? WEll make the dog sit first THEN throw.
BE SURE TO EXCERCISE each dog indivual, excercise, tug, walking, running , biting (toys of course) IS STRESS RELIEF.
Whistle dixie when YOU feel stressed, -act as if you just dont care-no over coddling, no oooo you poooor dogggy wooggggy pooo pooo -this makes YOU look like the weakest link ever! I say whistle for its hard to feel stressed and whistle at the same time, really it is!!
Crate, rotate, excercise, for ONE FULL MONTH.
Then have dogs out only on leash.. able to reach each other, but no ability to jump, hump, nip, command, reprimand each other. HAve humans in full control, just watch tv for a bit or sit on the porch , calm easy does it moments. NO TOYS. treats are ok..but dog have to sit, and take one small treat from human hand.. no competition.
remember YOU and all humans are IN CONTROL.
Once the dogs start to see that humans really are control you will see the tense start to leave their bodies, BUT, you also have to in this time really teach yourself what their stress signs are. (the dangerous poster was right you have to break this up BEFORE IT HAPPENS, not when the sheeet hits the fan=too late). But really learn what is the FIRST SIGN OF STRESS -baring teeth? TOO LATE, look for ears, tense shoulders, body tension, this is when you take command,
IF on leash, you see one dog being tense, just take the leash (leash is THE no.1 best way to control your dog), and walk away or have the dogs just walk in opposite directions, no need to yell, hit, flip out, JUST CONTROL the moment, walk in a circle or two with the dog, and just WHISTLE DIXIE (remember you dont care , you just are not going to allow any crazyness at all! ) CALM COOL COLLECTED this is you.
Then just keep doing easy peasy momemts , you want to end on a happy moment for all dogs. This hopefully will lead you to a path of calmness. But you will find that you will probably always have to be in control and it may be that your dogs will NEVER be able to romp and play together, some just CAN NOT. Its our job to learn their limitations and their boundries and stay within those safely and only venture out upon training .