Yes, one name they all can answer to, when in public or filling in forms etc is good. It would be easier if it's one on the birth certificate, or a nick name to that.

As for using "we" instead of "I" I would caution against that. In public -especially around people you work with- it might be noticed that you do that. Some insecure people do talk that way though, always using "we" when it's just them. If you can manage to consider them such as during therapy sessions, and say "we" when it truly is a "we" decision or event, that might help therapy move along.

Glad to see you are developing communication!