Multi Filter multiselect

Multi Filter multiselect

I am currently developing a resource manager for a group of shops and would like suggestions on how I can filter a 'Multiselect' field using a Lookup picklist listing area managers.

I have 4 affected zoho creator forms. 

resource_form
Field: available_to (lookup populated from  shops_form[shop_name])

shops_form
Field: shop_name (simple line text)
Field: area_manager (lookup populated from  manager_form)

manager_form
Field: name (simple text line)

order_resource_form
Field: multiselect (populated with shops selected in the  resource_form)
Field: area_manager (lookup populated from  manager_form)

I would like to sort the multiselect field within the order_resource_form to show shops belowing to each of the area managers. Any help extremely welcome.