Learn Portuguese (Portugal): Vocês são simpáticos, mas estão cansados.

São comes from the verb ser, which we use for permanent traits and characteristics, like someone's personality (simpáticos). Estão comes from estar, which we use for temporary states or conditions, like feeling tired (cansados) right now.

Since vocês means "you" (plural), why don't we use a "you" verb form?

In Portuguese, vocês means "you all", but it follows the same grammatical rules as "they" (eles or elas). That is why it pairs with the third-person plural verb forms são and estão.

Why do the adjectives simpáticos and cansados both end in -os here?

Adjectives must match the gender and number of the people they describe. Because vocês is plural, the adjectives are plural. The -os ending tells us this group of people is either all male or a mix of men and women. If the speaker were talking to a group of only women, it would be Vocês são simpáticas, mas estão cansadas.

Is simpáticos related to the English word "sympathetic"?