Hello, how I can enter more than one customer in the same invoice.
You cannot. One customer per invoice. If you have multiple customers sharing the cost you have to issue an invoice to each (or make each customer a sub-customer of a parent customer, but even then it is still one invoice per customer although a billed with parent can pay all teh sub-customer invoices)
Hello, you have mention in another post "do not have the child customers bill with the parent since it for whatever reason prohibits producing a statement for the tenant alone", but if there is more than one tenant in the lease, I should bill them all.