I would prefer singular characters as there is already six in total with my own bending group being part of the team.

However if you must then do so however please note that you will be in charge of all three characters (Fire, earth, and water), their arcs and character progression, and their manager if you choose to do so. I will not roleplay your characters for you I have a large work load as it is in my roleplay without adding in NPC's I was not planning on having in. I am choosing to have my other two benders' histories be revealed and will not be integral to the story as they have their own stuff to deal with just like Ren will. Ren is and shall be my main character for this roleplay but that doesn't mean I won't be additionally playing the other two as full characters. 

So in a quicker answer: Yes but I frown upon it because it's more likely to make a person quit if they have to juggle three characters as opposed to one.

For the later I prefer only one main character. This is just one group of people not two or three just one. I don't have plans for multiple groups in a single roleplay.