I have two characters near the beginning of my story, who are brother and sister. I want the reader to know right away, as the two are talking (they are alone), that they are brother and sister, but I'm not sure how to do this naturally without it coming across as forced.
How would two siblings address each other in a way it would automatically reveal their relationship? Could I write something like:
"Brother... are you sure we're on the right path?"
Or is that too "unnatural"? Would most siblings refer to each other by name? And to make the answers more universally helpful: what about other types of relationships (married, friends, associate)?