[JoeyP]

I think you and the people on here have hit the nail on the head
Yes... the one doing the aggrssive behavior is very likely doing it out of nervousness and insecurity
extra exercise will help
also redirecting their behavior is key
walk around with a favorite squeeky toy
a bag of treats
or a loud NO! or clap of the hands from you
anything to get them to stop in their tracks
it has to be loud ... and done once
no rushing and shouting their names
their attention must be redirected ..... then you go in and separate them