If your students are working in groups and you want them to submit into groups, first you need to set up these groups on the Moodle page
Go to This course, and select Group Management,
From here you can create the groups yourself, click Create group, give it a name, and Save changes,
To add to that group, click Add/remove users, and you can select the students you wish to add to the group, if you hold the ctrl key while selecting you can choose multiple students.
When adding users to the group, you should see a number after their name, thats how many groups they are in, so you can see easily who is already allocated to a group
Then when you are setting up an online submission link go to the Group submission settings
Change Students submit in groups to yes
Change Require group to make submission to yes
You do not need to change Require all group members to submit, this has been deactivited, meaning that only one member of the group needs to submit an assignment and this will submit it for all the members of the group.