In Gmail, I’ve “logged out all sessions”. Will this also log out all sessions of brand accounts?
Short answer: No.
Google Brand Accounts are accessed through a Google Account- By logging out of your account will not log out other users from their accounts, and will not block them to access the Brand Account.
If you are the owner of the Brand Account you could add/remove other accounts to help manage it.
There is no login/logout for Brand Accounts only for the Google Accounts that could be used to manage a Brand Account. If you log out of your Google Account then no others could use iT to access your Brand Account.