Learn Dutch: Wij zijn even actief als jullie. - We are as active as you all.

To say 'as active as', Dutch uses even (which means 'equally') followed by the adjective, and then als (which means 'as'). So even actief als literally translates to 'equally active as'.

Can I use net zo instead of even here?

Yes, you absolutely can! You could say Wij zijn net zo actief als jullie. There is no difference in meaning between even ... als and net zo ... als; both are very common ways to say that two things are exactly equal.

If I wanted to say 'as active as them' instead, would I use zij or hen after als?

You would use the subject pronoun zij (even actief als zij). When comparing subjects (like wij in this sentence), the pronoun after als must also be a subject pronoun. You are essentially saying 'as active as they are'.

Why doesn't the adjective actief get an -e at the end?

Adjectives only get an added -e when they are placed directly in front of a noun (like in de actieve groep). Because actief is used later in the sentence to describe wij after the verb zijn (to be), it stays in its basic dictionary form.