What parts are publicly visible?

The only publically visible part (which can be turned off) is the name of your group and a group picture. Here is an example of my family: The Gatewood Family Website

Why is this public? The public page is used to get all the members of the family into your group and that's it. Everything else inside the family website requires a member account to access. Once you have everyone in the site, I recommend turning off the public profile page.

Who can access the data? Only those you have granted access to your family website will be able to access all content in your site.

What can search engines see? The engines will only be able to see the group name and group picture if you set these to public. If you set these to private the search engines will be able to see nothing.