Hi Diane, Only people that you add to your "Trusted List" can edit profiles, and only those profiles that they are added to, so if you add someone to one profile's trusted list, it doesn't give them access to any other of your profiles. The only exception are profiles of people born before 1600, who are considered 'historically significant', and everyone who shares these ancestors is welcome to collaborate, as the privacy levels are "Open".
It's important, though to be willing to collaborate on your shared ancestors with other users, merging duplicate profiles, and working together toward WikiTree's mission of creating one worldwide collaborative family tree!