@beavontech, First, let me help you out with our split order flow. Our plugin will check whether the order has any product from a vendor. If that order does have any vendor product, then we will create a suborder with that product details. This order will be available to the vendor. Hence, no duplicate order is placed, they are just sub-order of the parent order.
The reason for adding this module is, every marketplace wants to become the next big marketplace giant like Amazone, Ebay etc. However, this becomes difficult for them due to some technical difficulties. That is why, for the last one year, WC Marketplace team is working on this solution, so our users can have the same modules like the big giants by just installing a single plugin. The split order module is one of the steps amongst them.
However, currently, there is no such way to stop sub-order creation. Because, based on this, we will add the next big modules too.
Let us know if you have any further query.