Coming from a people who are supposedly so family-loving, it may be surprising that the Italians have this little proverb: parenti serpenti, fratelli coltelli. Which means: relatives are snakes, siblings are knives. Not an entirely idyllic view of kin. Not entirely unrealistic either.
To illustrate our cynical little saying, I've chosen the wildly popular video of two Brit kids, where the baby is already biting big brother (like a snake, probably can't handle a knife yet), then giving a little gleeful laugh. Love the elder boy, who's already developed his stiff upper lip- he starts to cry, but then changes his mind.