In terms of how the data is stored and accessed, there's a limit to how much technical information that it's appropriate to give on a public forum, because this information could also be used by the wrong type of people.
Nonetheless to answer your question specifically, other than yourself and people you invite, in theory I (Gideon Greenspan) personally could have access to your stored information. In practise I only access a user's information for confirming identity as part of an account recovery process (if someone has forgotten their password and no longer has access to their old email address) or, with a user's specific permission, to debug a technical issue.
The data is stored in the USA at a well-known and reputable hosting provider. In theory someone there could also read your personal information, although this would have to be a direct and deliberate process considering how your information is stored.
Patterns of first names (only) appearing together in family trees are also aggregated statistically and anonymously to provide baby name recommendations on Magic Baby Names (www.magicbabynames.com).
I hope this answers the question?
