How to setup the workflow:
Manually create a merge from the order overview
When the bulk action is selected in the order overview, you are presented with an option to select which order is going to be the parent order. All other selected orders will then be merged into this parent order. The orders being merged into the parent order, will be set to CANCELLED alongside a message in the log on both the child and parent orders, mentioning that a merge has happened.
Only the parent order will be fulfilled in the shop system.