Only way I have found to do this is by desktop browser. Go to Gmail and sign in. On the top left hand side of the account click Gmail and choose contacts. In the contacts page you pick your group in the pull down menu on the left, choose group.
Near the top of the contacts there is an edit pencil, another icon, and a envelope icon. Click on the envelope and it will send to your group.
There is an app to do this but I can't find the play store link.
Sent using my Verizon Turbo charged 64GB Ballistic Nylon phone unfortunately with a case on back