If the group is indeed small, there is a simple workaround that can be helpful (Tiresome for many folks). Since the documents are shared and by default there is no way to know who has a doc open, you can agree to flag the doc by right-clicking and using RENAME... then including your name initials. Example:
Document.doc (original file name)
John Smith is going to edit the file but doesn't want to create a conflict copy. He renames the file to:
Then opens the doc, and works on it. Mary Brown opens the shared Dropbox folder and sees the initials JS, so she understands that John has the doc open and she decides to work on another file in the meantime. After 10 minutes, John's done, he closes the file and renames back to Document.doc... now Mary sees the doc has no initials, so she renames the file to MB-Document, then allowing John and the other team members to notice she's editing the file, and so on. Requires team discipline.