Three Labs and a Jack Russell Terrier

Question
I have 3 labs - two 5yrs and one 2.5 yrs. old. My sister had a Jack Russell, his name is Bounce, which they got as a puppy. He had often come over for play time visits and when my sister was out of town he stayed with us. Everyone got along great. When my sister realized she did not have the time to devote to Bounce we were helping to get him adopted. During that time he was staying with us and everything was going so well for a couple months, so we decided to keep him. We've had him for several months now and only just recently he has started to become aggressive with 2 of the labs. Occasionally, out of nowhere he just snaps and it turns into a vicious snarling match which usually requires me to dive in and pry them apart. I'm not even sure what triggers it. It just happens, no warning.

My father stays with them during the day and he mentioned that they don't get into any scuffles when I'm not around. I am certainly a part of the equation but not sure how/what I need to do next.

I am curious to hear from an expert in this breed if there is hope for all of them to live in harmony or if I am fooling myself. I do have a good understanding of the Jack Russell from what I've researched, but I have never owned one before. I want to do what's right for him and the others. He's a great dog and we have a great life together outside of this new behavior. I certainly need to be trained in dealing with this situation, but curious to know your opinion, realizing he is in a pretty competitive environment considering their all males and there are 4 of them!

Look forward you your response.

Answer
Tricia -

I would have been surprised if you told me you did not have this problem.

Jack russells just do not understand that they are small, so any time another, bigger, dog tries to boss them around, be alpha over them, or even just accidentally plows them over or bumps them, they will react assertively.

I can no longer foster male dogs because my jack (a rescue from a shelter where he had been for 8 months) will fight with them.  He will fight with my gordon setter female too when she gets too pushy with him, but I have no trouble with him with female cairn fosters because he does not see them as a threat to his "status."

Even if everyone is neutered (and has been for a while) I would not expect this problem to resolve without a ton of training for all of the dogs and keeping them on a very tight control method all the time.

I know this is not what you probably wanted to hear.... but the honeymoon period is over and now Bounce is trying to rearrange the pack dynamics, and is not likely to stop asserting himself.

-Beth