[Discussion] Blood Relations, Please?

[yaoi-queen.livejournal.com]

This may seem like a stupid question, but it's been nagging at me for quite awhile. Could someone tell me who exactly is related by blood to whom? I see the word 'brother' and 'sister' used so loosely in many fics and in the comic/anime (I know the japanese use brother and sister as an endearing nickname for someone close), but I'd like to know who are actually related.

The ones I already know are: The Italian brothers and German brothers.

Any help is greatly appreciated. :)

Edit: Thanks everyone for commenting! :D I've come to the conclusion that everyone is just as confused about this subject as I am. XD We can only hope Hidekaz clears this subject up in the future.