We have 2 manufacturing locations in China and 1 warehouse in Holland.
We set those up as 3 warehouses so that every location can have stock and its manufacturing orders. I have set this up with replenishment rules and resupply from routes, this is working correctly now.

But a new situation occurs as we also going to manufacture in our Holland warehouse.

 
The new situation is as follows;
When a new sales order has been placed for example 10 pieces of product X. We would like to produce 5 of those in our Holland warehouse and 5 in a Chinese warehouse. But still keeping one invoice for the customer.

 
I have thought about choosing a different route per quantity on the sales order, but only one route per product can be selected when creating a sales order.

Another thought was creating manufacturing orders at the Holland warehouse before creating the actual sales order. As the flow is that the stock is checked, if not available the product is resupplied (manufactured) from one of the Chinese warehouses. But this will give a lot of manual handling which can cause errors.

The third thought was duplicating the product, as that gives me the options I need to have to set up the manufacturing flow on the Holland warehouse. But will show as 2 separated lines on the customer's invoice, which is confusing in the end... So also not a solution as well...

Hope you guys can give this a thought and think out of the box with me,