There is a section at the top of the screen that allows the Skipper to add, delete and change Custom Groups. Once added, the groups appear in a column with check boxes by each crew so they may be selectively added to the group. This picture below shows the new sections annotated.
Once added to the group, the Skipper Send Email page available from the Skipper menu for a logged in Skipper will include that group in the To: dropdown.