The Main person is the person who is signed in. If your cousin signs in with his/her email then he/she will be the main person for that session. If we cannot find the signed-in person in the tree then we use the designated main person.
Having said that, we are working on giving you the option set up your site so that it uses the designated main person regardless of who has signed in. This feature should be out in a week or so.
And I like the other changes.