Final answer:
The subject pronoun to address two adults in Spanish is ustedes.
Step-by-step explanation:
The subject pronoun that you would use to address two adults is ustedes. In Spanish, ustedes is the second person plural subject pronoun, equivalent to 'you all' or 'you guys' in English. It is a formal pronoun used to address two or more adults in a respectful manner.
Learn more about Personal pronouns in Spanish