Delivery should be related to order because you can find the customer from an order, but you cannot find the order from a delivery.

Also, in the example I gave, there is no need to have a customer_id foreign key because you can find the customer from an order
[delivery]
delivery_id
order_id
emp_id

And employees should be renamed personnel (have you ever heard management say "do you have any employees on hand?"). Also, employees can be customers as well etc.