Select users with Read Only and Read Write Privileges

Hello Everyone,

I have come across a requirement for a new app for a secure documents app.

When a user uploads the doc, in the add / edit page they need to select from a drop down first all users that have read / write privileges.

Then below the above drop down, there is a second drop down that shows the rest of the users not selected. User then can select users that have read only privileges.

If any user is not selected from the two drop downs above, they cannot see the secure document in the list page and cannot access it.

I have attached a graphic that is close to what they are looking for.
Looking for any direction on how to populate the the drop down lists to mark the file as read / write and read /only access and then display it correctly in the list page.
Thanks in advance for any ideas.
Paul