new member problem with my Jacks

[rob]

Hello everyone,i am new to the forum and relatively new to dog ownership.I have two Jack Russell's both dogs(brothers) who are 14 months old,that were castrated at 12 months.
They seem to be developing a minor aggression problem and i wonder if anyone could help.
At the moment they are rarely left alone and when at home are very well behaved for there age apart from the occasional ruff and tumble that can get out of hand if left unchecked.
we generally walk in a group of dogs in the mornings all types and sizes numbers vary from day to day and there are usually no problems.
There have been three instances where they have jointly been aggressive towards other dogs by way of barking loudly at the other dog in close proximity as if they are trying to provoke a reaction, twice this has been with puppies who have been submissive and laid on their back.If i do not intervene the barking turns into snapping/biting although not rough enough to draw blood.The third occasion was with a large Staffordshire bull terrier (dog) who was obviously not submissive although very patient considering they were biting at his neck and ears.All three of these dogs where outside of the group we walk in.
Everything else seems to be fine they eat well one is a little greedier than the other i feed them twice a day on a dry mix supplemented with fresh cooked meat occasionally.
I would like to address this problem before it gets out of hand and look forward to your comments.

Rob