In this article the conflicts and alliances between different Dukes of Pastrana, lords of a Grandee household, and their relatives are analysed from two viewpoints. The first perspective shows how litigation between early-modern aristocratic siblings for family inheritance was a very common phenomenon. Secondly, litigious kin were allies in the political and social arena. With these features in mind, this paper provides an explanation of aristocratic behaviour as the consequence of the composite nature of aristocratic identity and the two juridical bodies used by the elites. According to this juridical theory, sovereigns were juridically composed of two bodies. The first one was political, representing eternal royalty. The second one was natural, meaning the physical person of each king. As will be stated in the article, this royal conception of the two bodies was adopted by the nobility and played an important role in aristocratic family conflicts. [ABSTRACT FROM AUTHOR]