As the Admin. Of my family research, When I add a member I thought they couldn't edit the work on the site? I had a member edit a entry on the site yesterday? The good thing is he is a cousin who I asked to join to make sure my Info. was correct.
You can also prevent people from editing site content by going to Setting tab > Privacy & change the settings for "Can site members edit the family tree" & "Can site members post content on the site".
Personally, I don't advise doing that. The fact people you invite can add data helps you.
Family sites are meant to be collaborative so by default, the site members that you invite (not just everybody) *can* edit the information and improve it. If you are not interested in them changing anything, please instruct them not to do this, either in the welcome message of the site, or by sending all site members a message (via Home > Site Members > Send e-mail to all members). There is also a setting that prevents site members from making changes so only you could make them. It is not working properly and we intend to fix it soon.
PS: you posted this item in the wrong place in the forums. It will be moved soon.