I'm not a tetra expert, but 8 of each would complete individual schools for both. I would bet the would intermix sometimes. I have 10 cardinal and they often divide themselves up. 5 mostly stick together, but a couple turned rogue and hang out separate from the others. The remaining bounce back and forth between the two groups. Every now and then, all of them are together.
Social behavior in fishes can be similar to humans. You have your close friends, some you see every now and then, and others are like relatives... fine in small doses.