The role of possessive adjectives with family members

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When I teach Italian, I say that we always use article before possessive adjectives but I know that it’s false! After one or two lessons I rectify my statement and I say that normally we never use article before possessive adjectives which refer to singular nouns (except with “loro“) regarding family members like padre, madre, nonno, nonna, zio, zia, cugino, fretello, sorella etc.
example:

mio padre
tua sorella
sua madre
nostro zio
vostra cugina
but
il loro nonno

We use the article with family nouns relating to: definite family members (nonno paterno, nonna materna), altered nouns (sorellina, fretellino), colloqial nouns (mamma, papà), plural family members (genitori, figli, nipoti) and the possessive adjective loro (singular and plural).
Now, try to write your family tree using this grammar rule.