[Rusty]

'They' or 'you (plural)' is an acceptable English subject pronoun for that conjugation, but not 'you (singular, formal)' or 'you (singular, familiar)'.

The Spanish second person has the following singular pronouns: tú and usted (vos is used in some countries instead of tú)
It has the following plural pronouns: vosotros,-as and ustedes

The conjugation entendieron is both a second- and a third-person plural construct. It is a second-person construct when the subject pronoun is ustedes. It's a third-person construct when the subject pronoun is ellos or ellas.

In Spain, the second-person plural familiar form is vosostros,-as entendisteis, but in Latin America, the second-person plural familiar form is ustedes entendieron.