How can I make a way of communicating that only family understands understandable to others too?

The cues family can read (a particular voice, gesture, gaze) are an important foundation of communication. To make them understandable to others: (1) compile "this cue equals this meaning" in a list or support book, (2) replace frequently used requests with shared means like photos, picture cards, or signs, and (3) share with those involved so everyone responds the same way. Rather than relying solely on family as "interpreters," gradually increase the means by which the child can communicate to anyone.