When do you use the article with possessive adjectives? And when do you omit?

The general rule of thumb with Italian is that possessive adjectives use a definite article alongside them (e.g. il mio libro, la sua macchina). The only exception to this rule is with family members, where the article is omitted (e.g. mio zio, sua madre, suo fratello.) NB. With plural family members, the article is put back in e.g. i miei genitori, le sue sorelle NB2. With 'loro', the article is put back in as well e.g. il loro padre, la loro nonna