Estate of Denial:  In the rush to button down an estate plan, people often spend most of their time focusing on the big questions and overlook small—but increasingly crucial—details.

Even the simple question of who your heirs will be is getting more complicated. Nowadays more people are considering pets and even children posthumously conceived from genetic material in their estate-planning mix, say financial advisers. That often means setting up trusts that just a few years ago would have been unthinkable.