U can create single invoice for multiple deliveries if the following conditions are met
1)payment terms are same
2)billing dates are all same
Go to VF01 and enter all the delivery document numbers and it will create a single invoice.
Or else goto VF04 and search all delivery documents,select it and click on collective billing document button. One single invoice will be created
Check with the functional consultant , what is the splitting criteria he has set for invoices,, if multiple deliveries are having same valuess in spliting field (ZUKRI) then only one invoice will be created,, otherwise multiple invoices will be created.