My first guess is that there exist human languages in which there's a distinctive word for that relation. (French, for example, has "cousin/cousine" for a male cousin or female cousin, which is about halfway there.) I would guess this is used when translating into those languages.
(I'm not especially expert here, but figured I'd mention this because nobody else had yet.)
To me, many of these words sound like almost childish terms of endearment -- a little charming.
Anyway, this is not at all academic for someone who wants to participate in the culture, because everyone around you is going to be identified and addressed in this way, and you're going to have to know who everybody is! Even if, in your head, "chacha" is not some abstract relation, but a particular person.
