Learn Dutch: Ze zijn over het project aan het denken. - They are thinking about the project.

In Dutch, you form the present continuous (doing something right now) by using a form of the verb zijn (to be) + aan het + the full dictionary form of the action verb (the infinitive). Here, zijn (are) pairs with aan het denken to mean "are thinking".

Why is over het project right in the middle of the sentence? Why not at the end?

In a Dutch zijn aan het sentence, the aan het + action verb almost always goes at the very end of the sentence. This means any extra details, like what they are thinking about (over het project), get squeezed into the middle between the verb zijn and the action aan het denken.

Ze can mean "she" or "they". How do we know it means "they" here?

You have to look at the verb right next to it! Because the verb is zijn (the plural form "are"), we know ze must mean "they". If it meant "she is thinking", the sentence would start with the singular form: Ze is.

Does the preposition over translate to "about" here?

Yes! Just like in English where you "think about" a topic, in Dutch you usually use denken over when considering or pondering something. You might also sometimes see denken aan, which is closer to "thinking of" someone or something.