To give edit access on a scenario planning draft to a person who has view-only access, change their user permissions under Manage > Roles.
For a building draft, the person needs the Manage scenario planning permission for the building. For a floor draft from the Edit floor menu, they need the Assign desks and Delegate desks permissions for every desk on the floor.
All users who collaborate on the same draft see the same queue and can work on it at the same time.
Lock a draft
Editors can lock a draft. A locked draft blocks edits from users with Collaborator access. Users with Editor privileges must unlock the draft before anyone can edit or publish it.