If I am understanding your question correctly, you are asking how your subcontract operation can create a material that can be consumed during your in-house operations. This requires two (2) Production Orders (or Lines).
Separating out the Sub-Contract process onto its own Production Order. This allows you to purchase Raw Material to (or transfer to) the Sub-Contractor Location (if needed), and the Output of the Sub-Contract Production Order can land in your SFG Location (or transferred from sub-location).
The second Production Order is for your internal processes. It will consume the Output of the first Production Order as raw material in the production of your true Finished Good.
If you want to keep everything on one Production Order, set both Output Items to a Manufacturing Policy of "Make-to-Order" and it will nest the Sub-Contract production as a second line on the Finished Good's Production Order.
Your BC Partner should be able to provide you with training on this setup within the Manufacturing module.