I treat group interviews like I am mingling at a bar or party. That helps minimize the anxiety. I think these group interviews are about seeing how well everyone will mesh together, so I focus on being friendly and keeping things conversational.

Don't stress about having to remember some random detail. If they ask a question you don't know the answer to, it's okay to say that you don't know. You can say something like 'I can't remember off the top of my head, but I would refer to X to refresh my memory' to illustrate that you know how to acquire information.