Any survey can be assigned to everyone in a group.
This means you do not have to manually assign the survey to each participant individually. When you make the Group Assignment it will be assigned to everyone in that group at that time, over riding individual participant settings.
Note: Participants added to the group after the assignment is made will not receive the assignment, you will need to re-assign the survey.
Start from the My Surveys page of any member of the group to which you wish to assign the survey.
When you click the Assign a Survey icon
make sure to select the group from the Group Menu.
This will deactivate the Respondent Menu, setting all participants in the group as the respondents.
Complete the assignment as you would any other:
Click here for details on assigning surveys to individuals, then follow the steps below for groups.
If you then add new people to the group simply re-open the survey assignment box 
and again press the button "Create Schedule from Parameters", there is no need to change anything else.
To delete a group assignment open up the EDIT box for the survey assignment and click "Delete Group Assignment". This will delete the assignment from every member of the group.