VAT Categories, some items is exempted from VAT

We are working in Medical sector and we have three different types of VAT categories

1- normal VAT category which is 15%
2- in the same invoice we can have some items with zero vat (for medicine items) and some other items with 15% for other items.
3- some invoices with zero vat items for Saudi patients, however for None Saudi patients we apply normal VAT 15%.

how to apply the three scenarios ?