In certain monarchies where voluntary abdication is the norm, such as the Netherlands, a royal family may also include one or more former monarchs. There is often a distinction between persons of the blood royal and those that marry into the royal family. In certain instances, such as in Canada, the royal family is defined by who holds the titles Majesty and Royal Highness.[1]Under most systems, only persons in the first category are dynasts, that is, potential successors to the throne (unless the member of the latter category is also in line to the throne in their own right, a frequent occurrence in royal families which frequently intermarry). This is not always observed; some monarchies have operated by the principle of jure uxoris.
In addition certain relatives of the monarch (by blood or marriage) possess special privileges and are subject to certain statutes, conventions, or special common law. The precise functions of a royal family vary depending on whether the polity in question is an absolute monarchy, a constitutional monarchy, or somewhere in between. In certain monarchies, such as that found in Saudi Arabia or Kuwait, or in political systems where the monarch actually exercises executive power, such as in Jordan, it is not uncommon for the members of a royal family to hold important government posts or military commands. In most constitutional monarchies, however, members of a royal family perform certain public, social, or ceremonial functions, but refrain from any involvement in electoral politics or the actual governance of the country. - WIkipedia
