Accomplish permission separation with external storage

Hello,
i have my nextcloud (18.7) instance on my NAS, where i have in separate folder my music, video and pictures, i would like to have access to those directory on nextcloud but if i add those external storage as system wide (local) i can only choose who have access to all the folder inside the external storage,
for example i have a Pictures folder, and inside all the album folders
is it possible to share with others the access to the external storage, but then decide which folder inside is shared ?

ex.

my structure is:
/Pictures
/Pictures/2018-holiday
/Pictures/2017-birthday

and so on, i would like that my family group have access to that Picture storage (add files), but for example can only see the 2017-birthday folder and not the 2018-holiday

i’ve tried to add the storage as user but i’m unable to mount local type.

any suggestion on how to achieve this?

thanks

EDIT:
i’ve found that i can share single directory, but i will loose the /Pictures/ structure

You could work with access control settings and workflows

You could tag the forbidden folders and set rules when access is denied.

In my example users other than admins are not able to access folders tagged with future.
Others can see the folder, but as soon as they try to access it they get This operation is forbidden

Photos
├── 2042 - Faster than light
└── 3042 - New Star is born  <<-- tagged with "future"

Great idea, i’ve never used the access control, i’ll give it a test!