Learn German: Wir haben alle Verwandten eingeladen.

The noun Verwandten is a nominalized adjective, meaning it comes from the adjective verwandt (related) but acts as a noun. Because it behaves like an adjective, it still takes adjective endings. After the plural word alle, it gets the weak plural ending -en.

Would the ending change if we dropped the word alle?

Yes! If you just said that we invited relatives without a determiner like alle, it would take the strong adjective ending for the accusative plural, which is -e. The sentence would simply be: Wir haben Verwandte eingeladen.

Is a nominalized adjective like Verwandten always capitalized?

Yes. Even though it changes its endings just like a normal adjective, it is officially functioning as a noun in the sentence. Because all German nouns are capitalized, this word must always start with a capital letter too.

What case is alle Verwandten in this sentence?

It is in the accusative case, because the relatives are the direct object receiving the action of being invited. For plural nominalized adjectives, the accusative endings are exactly the same as the nominative endings.

Why does the past participle eingeladen have the -ge- in the middle?