Corydoras of any species will play better with others of the identical species but I have never seen any cory threaten any other fish, including other species of Corydoras. If you cannot get enough of a single species for a nice playful group, there is no reason to subject another small group of another species to the same fate of only being present in small numbers. I personally prefer groups of 6 or more of a single species of cory to bring out the playful nature of these gregarious fishes. Some of the best responses that I have seen from them is when I kept at least 10 of a single species in a tank.