My kids call each other by their names and other nicknames they've aquired for each other.......But when they're friends ask the older answers "Never seen him before." And the younger answers. "what person I don't see anyone there." But I have heard them say "he's my bro." and as for their sister they answer. "She our little sis." I'm guessing because of her stature.
I've always said my carnala. or my sis. even tho she's only half my sister.