When you create a shared folder and allow member to have view-only permissions, they can view and comment on files in a shared folder, but not add, edit, or delete files. You can find more info about this here.
Hope this helped. Let me know if you have any other questions!
I have a similar permissions issue, but not quite the same issue.
I have created a folder (at top tier level) that I have shared "Read Only" with 6 other people. One of those persons wanted to add some information (as a subfolder in that top tier level), but was unable to (I assume because it was Read Only), but was able to create a a new folder with her as the Owner -- in my account!