fish aggression

I have a kelberi that’s around 3-4” and just added two 5-6” spider kelberi, they’re probably about twice his size.. should I be worried about them eating him? At what size comparison would I have to stop worrying about this? I currently have a divider up with the smaller one separated from them

Recently I've moved back into my dorm with my 10 gal tank of dace and darters. 3 rainbow darters, 2 fantail, and 4 blacknose dace and 2 s. redbelly. Before they came home with me everyone got along well, and my dad said everything was fine when they were with him. They did go through a...