When you draft a health care proxy, the goal is to pick an agent who will then act on your behalf. If you cannot make medical decisions, they make them for you.
In some cases, estate disputes start because of sibling rivalry. The way that kids have related to each other all their lives can continue even into adulthood. This can make them compete with one another or resent each other. Those feelings come back up when they do not agree with a will or estate plan.