I don't know if this will help make it any clearer. It really depends on whether or not they are on the 'Trusted List' of a profile. If they are on the Trusted List of every profile for which you are manager - they can see everything you can, and edit as well. If they are not on a Trusted List of a particular profile, they get the same view as described in the Privacy Levels page.
Did you add them both to the Trusted List of all your profiles? or just a partial list?
Example: My cousins, on my mother's side, don't necessarily have interest in my fathers' ancestors - they are interested in their own father's ancestors. So I added them to the Trusted lists on my mom's family line - her parents/grandparents etc, but not my Dads.
If I add you to my Trusted List can you access every profile I can access?
No. Every profile has its own Trusted List. As a WikiTree user, you have a profile and your profile has a Trusted List. People on this list can access your profile but they cannot automatically access other profiles you have created or edited. Those other profiles have their own Trusted Lists.
You might want your sister on all of them - but then if you are married and have a substantial set of profiles on your husband's family, going back generations - she might not have an interest there - so you wouldn't necessarily add her to the Trusted List of those profiles. Same with your cousin - you can add him to those profiles with a family connection to him.
When you look at the Privacy Levels page - it tells what can be seen by others. A few of the higher Privacy Levels indicate you must be on the Trusted List to see more.