Perhaps brother and sister don't need to be shown under related...

Perhaps brother and sister don't need to be shown under related party transactions, whereas parent and child, or spouse certainly do.

Just researching that now, but there's plenty on it.

http://www.allens.com.au/pubs/cg/focg21apr11.htm

http://www.minterellison.com/Pub/NL/201109_CHQd/

Aha, brother and sister DO count according to this PDF file

"10.9 Relative – in relation to an individual, means the spouse, son,
daughter, brother, sister, father and mother who may be expected
to influence, or be influenced by, that individual in his/her dealings
with the reporting enterprise."

No, that was an India government release I saw later!

Haven't found a definitive one for Australian Corporations Act yet, and have to move on for a while. Maybe someone else can keep going?