Members of a family site have full editing privileges for that particular site.
To restrict your members so that they cannot edit the family tree, please do the following:
Open your family tree on your family site.
Go to Family Tree > Manage trees.
Choose ‘Edit tree settings’.
Under the option ’Specify below who can edit the family tree on the family site:’, make sure to choose that only you can edit the tree.
Save your settings.
You can choose whether or not to give your members the privilege to invite people to your family site. Mouse over your name in the upper right corner of the screen and select “My Privacy”.
Select your family site from the list on the left and click “Access”. Remove the check from the check box ”Allow members to invite other members to your site”.
Make sure to save your settings!