Pristella Tetra acting aggressive and minor stocking question?

Hello I've been watching my fish and noticing one of my Pristella Tetra has been acting a little aggressive amongst my fish. I have 2 guppies, 2 neon tetras, and 3 pristella tetra. First off I had 5 neons and slowly but surely they've been dying one by one unfortunately. So the aggressive fish will sometimes chase the other ones to the other side of the 10 gallon, but sometimes it's chill, and sometimes may chase others a little. I know fish determine a pecking order so is it most likely just establishing dominance and nothing further. I hate having aggressive fish that kill the other ones. I was thinking of filling out the neon and pristella tetra schools, any suggestions would help?