Instead of using passwords on sub-folders, I did it by setting membership levels for the sub-folders: owner, full member, junior member, guest
(On my site they're labeled owner, family, friend, anyone)
These choices appear whenever I create or edit any folder and photo.
If, when you are logged in as the administrator, and you try to create an album or edit descriptions, you can see the "Who can view this photo" pulldown, then you can use this approach.