What is the difference between anata and anatatachi?

What is the difference between anata and anatatachi?

Anatatachi is the plural version of anata. The tachi suffix in general pluralizes whatever group of people you put it after.

Yep, basically the same as “you” verses “you all”
Here’s a few other examples
私(わたし): I, me
私たち: Us, we
生徒(せいと):pupil
生徒たち:pupils
etc. etc.