Since Mamá y Papá can be replaced by the subject pronoun that matches the third person plural, which is ellos, then we must choose the correct conjugation of the verb aprender that matches this person as well. So we have that:
aprendimos matches the first person plural (nosotros) in the simple present
aprendisteis matches the second person singular (vosotros) in the simple present
aprendió matches the third person singular (él/ella) and the formal you (usted) in the preterite.
aprendieron matches the third person plural (ellos/ellas) in the simple present.
Finally:
<em>Mama y Papa </em><em>aprendieron </em><em>a jugar al golf</em>
