A wallet acts by its own key, and nobody else may act for it unless it grants them a right: to send its tokens, to update its info, or everything as an admin. A token, storage or network account has no key: exactly one owner runs it, with any admins the owner names.
A token, storage or network account also has a default: what anyone may do without a right of their own, such as depositing into a storage account or holding a token. A right of one's own replaces the default rather than adding to it, so an empty right blocks.
A right can be given to the holders of a certificate rather than to an account: whoever holds a certificate from that issuer has it. A multisig's signers and quorum are set when it is created and can never change.
KTA