With BitPay's Business plan you can add multiple users to the BitPay dashboard. Each user will have individual login credentials (email and password).
Go to https://bitpay.com/dashboard/settings/users/invite to invite a new user to your BitPay dashboard and choose the set of privileges which shall be given to the new user.
The invite will be sent to the email address provided.
It contains a link which allows the user to create an account and set a password.
Each user can set up 2 Factor Authentication via https://bitpay.com/dashboard/user-settings/edit/security after creating their account (recommended).
The below screenshot shows what a user with support privileges would see if he logs into the BitPay merchant account. The support privilege allows him to view incoming payments but not to modify the account settings (settlement information for instance).