Antonio Matteo Originally, in middle age king or lord be twin or not, siblings were crowned princes, princess or titled lord, lady, duch or duchess. Most culture, the inheritance was sorted on birth rights where the oldest would took over responsibility as kings or the overlord. That being said, the oldest of the twin will take over the royal responsibilities and the youngest titled prince or princess.
In other culture, the title of Kings or emperor were directly entitled to the male primogeniture old or young, twin or single, like in the case of Japanese royal family or the gulf states royals.
In societies where the royals are polygynous, the status of the twins depends on which succession custom they follow. It might depend on the status of the mother (wife or concubine) &/or whom the father chose, or rotational where succession is to passed on to the next royal family; this is mostly follow in Africa.
