Brothers and sisters are trained fighters
Family fights were one of the reasons I was delighted to leave the world of auctions behind. Brothers and sisters who, for the most part, got along well, when mum and dad passed away, suddenly decided that the family couch was theirs for the keeping and were prepared to fight to the death for it. The same could be said for paintings, or books or even the pots and pans. There is never a real winner, it is always ugly and invariably there is collateral damage.
Often, decades of unresolved frustration boil over to turn even the most reasonable siblings into martial artists.
Strangely enough, these days, as I record Life Logs for various clients, this same theme crops up time and time again. People filled with regret or even remorse over fights about stupid possessions at the cost of a friendship with a sibling.