sus

determiner

1. his, her, its, their

   • Sus padres van a ser abuelos.
     His parents are going to be grandparents.

2. your (polite or plural)

   • ¿Cómo se llaman sus hijos?
     What are your children's names?

The plural of su, used before plural nouns.

Learn it in Unit 4: The family: More family: grandparents, uncles, cousins · A1