That is great the yours are getting along. Just keep an eye on them as it is more frequent than not. You will have to learn to know when they are just nipping or it is all out aggression. Mine will nip at the others when they are feeding but that is all. Good Luck with your new '' brood''.
If you can give them plenty of room they should do fine. When they get crowded they get a little more aggresive. Keep the water clean and the turtles fed and they should do fine.