Go to your contacts and create labels.
Then group your contacts by labeling them.
Now when composing a new email instead of adding the contacts one by one you can use the label name.
All the contacts under the selected label will be auto added.
Adding multiple labels, all contacts under each label will be added.
(following the comment)
Sorry @marikamitsos if I wasn't clear. Me with my friends want to create an "email address" that when someone send a mail to it, all of us receive the sent mail.
As stated in the official Google help page
Forward to more than one account
You can only automatically forward all your messages to one account.