The sabertooth tetra is quite a nervous fish and it needs a really big tank with some heavy duty filtration and water flow to feel at home..and still they tend to die when they reach a certain size...no one really knows why, with any certainty.
If i were you i would keep snakeheads in their own tank..they are great fish with an distinct personality and i think they deserve to have a tank all for them self..of cause that is just my personal opinion