I have schools of 8 cardinals and 4 danios. The danios school together, chase each other like psychos and leave the tetras alone for the most part. Every once in a while one will chase a tetra or a guppy for a couple seconds and then go back to the group. I think they are a fun combination (color-tetras and action-danios). But I had to bump up the danio school only 2 didn't work they chased everything.
Good luck