Learn Portuguese (Portugal): A casa deles é bonita.

Deles literally means "of them". In Portuguese, words like dele, dela, deles, and delas tell us who the owner is. Because the owners here are a group of males (or a mixed group), we use deles. It does not change to match the feminine word casa. If the house belonged to a group of women, we would say A casa delas.

Why is the word order A casa deles instead of putting "their" before the noun like in English?

Because deles is made by combining the word de (of) and eles (them), it literally translates to "the house of them". Just like you wouldn't say "the of them house" in English, you must place deles after the noun in Portuguese.

Why does the sentence end with bonita instead of bonito?

Adjectives must match the noun they are describing. Here, the adjective is describing the house (casa), which is a feminine word. Therefore, we use the feminine form bonita. The masculine owners (deles) do not change the fact that the house itself is feminine!

Why do we use é instead of está for "is"?