The maps can be separated with permissions within one workspace, they don't need to be accessible (or even be seen) by everyone.
To move the maps from workspace A to workspace B, please follow these steps:
1. Make sure that you are a Member of both workspace A and B and you can create story maps.
2. Open workspace A.
3. Open '...' menu in the top-right corner and select Manage story maps.
4. Click on the Options menu on a story map's tile.
5. Select "Transfer to other workspace" from the menu.
If the Transfer option is missing, please check step 1.
6. Select the workspace you like to move the story map to then click "Transfer story map".
7. Repeat 4-6 with all the desired story maps.
The other way to transfer is directly from a story map. To do that, just open the story map you like to move and select Transfer from the story maps quick menu:
After that, everything is the same as it was described above.
8. Go to workspace B.
9. Open the story maps on workspace B and 'Share' them with the appropriate people in the new workspace. You might need to invite them into the new workspace.