Learn Italian: La loro stirpe è famosa in Italia. - Their lineage is famous in Italy.

You are remembering the rule where singular family members drop the definite article (like mio padre). However, the possessive loro is a major exception to this rule. It never drops the definite article, no matter what noun follows it. So, even if we were talking about a direct family member, it would still be la loro madre.

Does the word stirpe (lineage) count as a family member for the article-dropping rule anyway?

No, stirpe does not count as a family member. The dropping rule only applies to nouns for specific relatives (like mother, father, brother, aunt). Stirpe is a collective noun meaning lineage, ancestry, or descent. Because it is not a specific relative, it takes the definite article with any possessive, such as la mia stirpe (my lineage).

How do we know the gender of stirpe since it ends in -e?

Stirpe is a feminine noun, which is why it takes the feminine article La and the feminine adjective famosa. Nouns ending in -e can be masculine or feminine in Italian, so you often have to memorize them. Looking at the modifiers in the sentence is a great way to confirm the gender when you are unsure.

Why is the preposition in used without an article before Italia?