In so many families the kids polarize, right into adulthood. They cut each other off and let the childhood dynamics ruin the present and the future. It affects everyone, because where once there was a sibling (and aunt, uncle, cousins, etc.) now there is a ghost.
What do the children learn from this? To solve problem relationships in the same way. Is that what we want for our kids? The important thing to remember is the old adage: let bygones be bygones. Because once your parents are gone your sibling is the only person who lived, and survived, your history with you.