Horrible things happen. Incredible things happen. Other people exert their influence. People die. Events that bond one group of siblings will fracture and alienate another. There are simply too many variables in life for anyone with a conscience to claim, “Just do such-and-such, and your kids will turn out thus-and-so!” Beware such dangerous nonsense.
However, according to an extremely unscientific poll I conducted, parents can do some things — and avoid some things — to help influence their children so they will be more likely to remain friends with their siblings when they are adults.