On your email page, and the right end of the address bar you should see Cc and Bcc They are Carbon copy and Blank Carbon copy. If you type the other addresses in the Bcc box they will be visible to the individual recipients only, not to anyone else.
The address box at the top of the page. You have a SUBJECT box, at the right end of that you should see 'Show Cc and Bcc. Click on the Bcc and another address bar will open, the addresses you type into that will not show on the email.
Not that I've ever tried, but isn't it possible to create a group name and use it to send to all assigned to the group at once, without allowing anyone sight of individual members ? Just asking.