Learn Portuguese (Portugal): Elas não são médicas.

In Portuguese, there are two words for "they". Elas is specifically for a group of females. If the group was all males, or a mix of males and females, you would use eles.

Why do we use são here for "are"?

São is the form of the verb ser (to be) that goes with "they" (eles or elas) and "you all" (vocês). We use ser here because a profession is considered a permanent trait or identity.

Does the word não always go before the verb?

Yes! To make a sentence negative in Portuguese, you simply place não immediately before the verb. Here, it goes right before são.

Why is it médicas and not médicos?

Nouns for professions change to match the gender and number of the people they describe. Since the subject is elas (feminine, plural), the word médico (doctor) changes its ending to -a for feminine, and adds an -s for plural, becoming médicas.