Let's see. I think what you are calling "site manage" would be called a profile manager (PM) on the Wikitree. Each person represented on the Wikitree has a data dossier called a profile.
If you made your grandfather the PM of the Wikitree profiles that you have created then likely you (or him) is/are the PM. I don't see that you are connected to your grandfather when I look at the descendants in his family.
One solution would be to use a different email address and add it to your personal profile (maybe you've already done something like this?). This would create a new account for you on the Wikitree, however. Then from his profile "he" could add you to the trusted list and then make you the manager of those profiles.
However, as I explain this, I can see this is probably confusing and it might be best to just email firstname.lastname@example.org and explain what has happened. That's the experts and they'll help you. Tell us how it goes as often there are problems in the beginning but it will get easier. Good luck!