Depends. 1) If they are all still juveniles, then two will mature into adults (one male and one female), the third will stay a juvenile forever (unless one of the adults dies, then the juvenile will mature into an adult). No problems. This would be called a clown harem. 2) If all 3 are males, one will turn into a female, one will stay a male, and one will die. 3) If the two are a female and male, and the third (original) is a juvenile, no problem. The third will stay a juvenile forever. Again, this is a clown harem. 4) If the two are males, one will turn into a female, and the third will either die (another male) or live (still a juvenile). I think I covered all combos. As you can see, there is no definitive answer (yet). Only time will tell. What size are the two new ones, and what size is the third one (original)? If they are 1 inch or smaller, you'll probably be fine. If they are larger, well, good luck as anything could happen.