Do you need to be a member

You have to be a member, or get an invitation from a member. Yes, staying at the Magic Castle Hotel also includes posts for entry.

I think so or you need to go with someone is a member already

For what? If you want to visit you need a member to put your name on the list. There are also other ways to attend. I think staying at their hotel nextdoor can get you access. Either way check their website and call them for details.