Have the ability to have more than 1 'responsible user" per inventory item

We would like the ability to have more than 1 responsible user per inventory item, but at the same location. Currently you can only have 1 responsible user per item per 1 location. The only way around this is to have multiple locations for an item and set a user per location.

Ideally we would like the department head and vendor to be notified when an item goes below the minimum threshold.