How can I create an internal employees group that will receive a copy of all emails sent to our database?

You will need to create a lead for every employee that wants to receive those emails. Then, create a list (ex : internal employees) and make sure that every one of them is part of that list.

Add that list to all the lists affected by every new campaign (if that campaign is not activated by a trigger). It is important that every one of those leads match the campaign criteria or it will be excluded from the mailing by the decision tree.