When you create a new profile you are set as the profile manager.
To add managers to an existing profile:
To remove managers from a profile:
To change many profiles at once, use the Profile Manager Changes tool. You must be on a user's Trusted List to add/remove them from multiple profiles at once.
Hi, Francis
From your own profile, you can add your brother-in-law to all profiles in your Watchlist by using the help on this page: Trusted List Changes. You shouldn't make the changes from his profile since he isn't connected.