My students are working on a StoryMap. Two students created their own "Group" within the Group I had set up. They were able to collaborate within their Group, but couldn't upload their StoryMap to the Group I set up.
They can share to the group with access capabilities as long as they are a member of the group itself. Did you create the group? If so, make sure they are members and that members of the group can share items. You can find this in the Group Settings page. Then, when they are ready, they can go to their item's Item Details page and click the share button to choose the group to share the map with. Let me know if this helps!
