Filtering Properties


Can you please explain to me how to configure filtering of properties?

I have Object Type Customer, with a Sales Persons (multi-select) property.

When I create an object of type Documents, after I select de Customer, I want the Sales Person to list only those Sales Persons which are in the Customer Object.

I do not want to add on each Sales Person, a metadata to all the clients, because they have hundreds, maybe thousands of client.

Is there a way to filter them?