Learn Portuguese (Portugal): A aldeia onde viveu o meu avô materno é pequena. - The village where my maternal grandfather lived is small.

This is subject-verb inversion in a relative clause. While you could technically say onde o meu avô materno viveu, putting the verb first sounds much more natural in Portuguese. This inversion is very common in relative clauses, especially when the subject is long and the verb is just a single word. It prevents the verb from being orphaned at the very end of the clause.

Could I use em que instead of onde in this sentence?

Yes, em que or na qual would also be grammatically correct here to mean 'in which'. However, onde is the most natural and common choice when referring strictly to a physical, geographical location like a aldeia.

Why do we include the article o before meu avô materno?

As a quick refresher: in European Portuguese, it is standard practice to include the definite article (o, a, os, as) before a possessive pronoun. Leaving it out (saying just onde viveu meu avô) is grammatically possible but sounds heavily like Brazilian Portuguese.

Is it common to use formal-sounding terms like avô materno in casual conversation?

Yes! While English speakers rarely say 'maternal grandfather' outside of formal or medical contexts, Portuguese speakers frequently use avô materno and avó paterna in casual, everyday speech to efficiently specify which side of the family they are talking about.