While each situation is different, I think in most cases, the decedent should keep his family informed of his or her estate plan. If the decedent wants to treat his children or others differently, the decedent should communicate with that family member why. It may be because a family member has special needs or it may be because that family member has exhibited behavior that demands action. For example, if the family member has committed a crime or shown a tendency to bad behavior, it is reasonable to exclude or reduce that family members inheritance.
Notifying that family member should help avoid a will contest, or, if not, significantly improve the estate’s chances of a successful result in arbitration or litigation. Of course, the family member may file suit anyway, and the estate may end up settling the matter to avoid the costs of litigation. Nevertheless, in most cases, it is better to notify the family member in writing since the estate will then be in a much stronger position if a law suit is filed.