Learn Finnish: Veli tuo teidät tänne. - The brother brings you here.

Teidät is the accusative form of te (you, plural or formal). We use these special accusative forms for personal pronouns when they are the complete object of an action. Since the brother is bringing you, you are the object, making it teidät.

Could I use the partitive form teitä here instead?

You would use the partitive teitä if the action was just ongoing or incomplete. Using the accusative teidät shows that the action of bringing you is seen as a complete, finished event.

Why does the sentence use tänne for 'here' instead of täällä?

Finnish uses different words for location depending on movement. Täällä means being in a place (stationary here), while tänne means moving to a place (to here). Because the verb tuo (brings) involves movement to this location, we have to use tänne.

Where is the word for 'The' before brother?

Finnish does not have articles like 'a' or 'the'. The word veli simply means 'brother', 'a brother', or 'the brother'. You know it means 'the brother' here just from the context.